(1) Cotyla. (Cotyla, Ok. cup). In this work "cotyla" is used for a shallow concave articular surface (Howard, 1929; Lambrecht, 1933).

(2) Cartilago epiphysialis; Epiphysis; Diaphysis; Metaphysis. During development and growth of a long bone, ossification begins in the middle of the shaft  (Diaphysis), and extends proximally and distally by growth of ossifying zones (Metaphysis) into the cartilaginous end (Epiphysis). The epiphyses of birds, unlike mammals, do not ossify endochondrally from separate centers of ossification, but only by extension from the metaphysial centers.

(3) Os pneumaticum. Bone invaded by air sacs; the sacs are outgrowths of the lungs, tympanic cavity, or nasal cavity. Foramen pneumaticum; Pori pneumatici. In the paleontological literature the foramina are commonly known as "pneumatopores". The skull, vertebrae, and bones of limb girdles are usually pneumatic; limb bones are variably pneumatic in different taxa of birds. Pneumaticity usually involves only the proximal elements of the limb, but in some forms may extend into its distal extremity. Since pneumaticity is so widespread in the skeleton, the foramina and smaller pores are listed only for the bones in which they form especially distinctive features. See Annot. 6 and Resp. Annot. 70, 75-77.

(4) Pila (L. pillar or column). Pila refers to a reinforcing element of a bone that may form a distinct, prominent bar, or may be a thickening that blends almost imperceptibly into the bone of which it is a part.

(5) Scapus (L. shaft, stem). Used in this work to refer to a slender, attenuated bone or part of a bone in the instances that "corpus" (body) is not applicable (e.g., clavicle, pubis). See Integ. Partes pennae for another usage of Scapus.

(6) Os medullare. Female birds are unique in possessing a special system of highly labile, secondary (medullary) bone within the marrow cavities of much of the skeleton during the reproductive period. This bone grows as spicules into the medullary cavity from the endosteal surface, serving as a labile reserve of mineral that can be mobilized to provide calcium for egg shell formation. Taylor, et al. (1971) present an extensive review of medullary bone (see also Hodges, 1974). Os spongiosum. Spongy bone (also known as trabecular or cancellous bone) is found throughout the avian skeleton. In early postnatal life the spongy bone of the Calvaria (Diploe), vertebrae, limb bones, etc. is ftlled with red marrow (see Hodges,  1974). Later the red marrow is replaced by fatty marrow or by pneumatic mucosal diverticula invading the bones from the nasal or tympanic cavities (Stork, 1972; Warnke and Stork, 1977; Witmer, 1990) or lungs and air sacs. The Cellulae pneurnaticae are cavities or spaces, lined with mucosa, that are smooth-walled, e.g., long bones and skulls of nestlings, or highly strutted as in the skulls of adult birds. See Annot. 189; Resp. Annot. 21, 70, 72, 75-77.

(7) Tuberositas. (L. tuberosus, full of lumps). In anatomical usage "Tuberositas" usually refers to a roughened or knobby area of bone for attachment of tendons or   ligaments (Donath and Crawford, 1969).

(8a) Facies; Cranium. Following the Nomina Anatomica Veterinaria (ICYGAN,  1983), "Facies" is used in this work for the facial skeleton ("splanchnocranium"), and "Cranium" refers to the part of the head skeleton enclosing the brain ("neurocranium").

(8b) Ginglymus craniofacialis [G. nasofrontalis]. This term is trea'ted with the flexible zones of the skull in Arthr. Annot. 46.

(9) Fenestra antorbitalis (Heilmann, 1926). Synonymy: antorbital vacuity (Shufeldt, 1909); Hiatus orbitonasalis (NAA, 1979). When the skull is viewed from the side, this is the pronounced gap, often triangular, bounded by the nasal process of the maxillary bone, the maxillary process of the nasal bone, the jugal and lacrimaJ bones, closed by skin laterally (Fig. 4.1). It represents the antorbital vacuity of archosaurian reptiles (Witmer, 1987).  Fossa antorbitalis [F. infraorbital is ] .. The antorbital fossa is the space medial or deep to the Fenestra antorbitalis which houses the Sinus antorbitalis [Sinus infraorbitalis] (see Resp. Annot. 17), an evagination of the nasal cavity. The osseous walls of the Fossa are variable; often the palatine process of the maxilla, the palatine bone, and the ectethmoid  contribute to its walls (Witmer, 1987). Witmer maintains that the antorbital fenestra and fossa are completely homologous with those of non-avian archosaurs.   Fossa infraorbitalis is retained as an alternative term because of its widespread use.

(10) Hiatus craniofacialis septi. Synonymy: Fissura craniofacialis (Hofer, 1955).In the dried skull, the hiatus is the interval between the rostral edge of the interorbital septum and the caudal border of the osseous nasal septum in birds having such a septum (e.g., Anser). The hiatus' is completed by a septum of cartilage in intact specimens (Butendieck, 1980). Biihler, et al. (1988) state that this hiatus is characteristic of all modern prokinetic birds. as well as many neognathine rhynchokinetic birds. Paleognathines have a continuous nasal/interorbital septum. See Annot. 55.

(11) Arcus jugalis. Synonymy: Arcus zygomaticus. The jugal arch is a slender, generally straight, bar that connects the upper jaw with the quadrate bone (Figs. 4.2, 4); exceptions include a strongly sigmoid shape in some penguins and a laterally bowed shape in Nyclibeus and Caprimulgus. The arch consists of three ankylosed elements: Proc. jugalis of Os maxillare, Os jugale proper, and Os quadratojugale. See Arthr. Intro.

(12) Apertura nasi [nasaleJ ossea. Synonymy: Naris. The shape of the nasal aperture (schizo rhinal , holorhinal) is related to kinesis of the upper jaw (see Garrod,  1873; Hofer, 1955; Bock, 1964; Yudin, 1965; the reviews of Biihler 1981 and Zusi 1984). Some pelecaniform, sphenisciform, and other birds have paired, minute osseous apertures of the nasal cavity. See Resp. Annot. 1; Arthr. Zonae flexoriae. PHa supranasalis. The median column of bone making up the dorsal border of the external nares; formed by processes of the nasal and premaxillary bones. See Arthr. Fig. 2.

(13) Fenestra palatina. Synonymy: Fonticulus palatinus (Hofer, 1949). Oval or elongate opening in the rostral part of the bony palate between the two premaxillae. In birds such as Strix, Gallinula, and anseriforms, the fenestra is set off distinctly from the more caudal Fissura interpalatina. The two are confluent in, e.g., Diomedea, Calhanes, and Larus.

(14) Depressio frontalis. The frontal region (forehead) of the skull in some birds (e.g., Ardea, Anser) is indented by this shallow, longitudinal concavity (Fig. 4.6); in other birds the frontal region may be flat or dorsally convex. Crista frontalis interna. Median crest on the interior of the vault of the calvaria extending from the fossa of the olfactory bulb to the upper end of the cerebellar fossa. (15) Fossa glandulae nasalis. In certain birds the Glandula nasalis (so-called "salt gland ") occupies a pronounced depression on the dorsal aspect of the supraorbital margin of the orbit, involving mostly the frontal bone (e.g., penguins, albatrosses, loons, gulls). In others (e.g., pelecaniforms, grebes) the gland is intraorbital, i.e., ventral to the supraorbital wall of the orbit there occupying the shallow Impressio gl. nasalis (see Siegel-Causey (1990).

(16) Calvaria. The so-called cap or dome of the skull. Prominentia cerebellaris (Shufeldt, 1909). The external, median convexity of Os supraoccipitale and Os parietale in the nuchal region of the skull dorsal to the Foramen magnum (Figs. 4.4, 5). The prominence overlies the dorsum of the Cerebellum, reflecting its contour externally, e.g., Buteo, Columba, Corvus, and trochilids. See Annot. 17.

(17) Crista [Linea] nuchalis sagittalis. This median crest is dorsal to the Foramen magnum, and provides attachment for thel sheet of deep fascia separating the right and left columns- of dorsal neck muscles. The Crista surmounts the Prominentia cerebellaris in some forms (e.g., Gavia, Morus). Crista [Linea] nuchalis transversa. Synonymy: Crista temporal is (Hofer, 1945); Crista occipitalis (Davids, 1952). Arched, usually distinct, crest separating the nuchal plane of the supraoccipital bone (for attachment of the neck muscles) from the smoother part of the calvaria (parietal and squamosal bones) farther rostrally (Figs. 4.1, 5). This crest may extend caudolaterad to reach Proc. paroccipitalis (Annot. 85) (Figs. 4.2, 3).

(18) Foramen magnum. Synonymy: Foramen occipitale magnum. The opening in the base of the skull that transmits the spinal cord and its meninges; it is bounded by the supra-, ex-, and basioccipital bones. Duijm (1951) reviewed the position and plane of the Foramen magnum in the major skull types of birds.

(19) Meatus acusticus externus. Synonymy: Fossa auricularis cutanea (Freund, 1926). The wall of the Meatus is formed mostly by cutaneous, fibrous, and cartilaginous tissues. The osseous wall of the Meatus is formed by the parasphenoid ala (Annot. 20), lateral margin of the paroccipital process, and Crista tympanica of the body of the quadrate bone (see Arthr. Annot. 37).

(20) Hiatus subtympanicus. Synonymy: Hiatus alae tympanicae (NAA, 1979). Deficiency (notch or fenestra) in the junctional area between the Ala parasphenoidalis and the margin of Proc. paroccipitalis that partially bounds the external acoustic meatus. See Annot. 19, 84.

(21) Cavum tympanicum [Cavitas tympaniea]. The middle ear cavity consists of a shallow, open concavity in the dried skull. Owing to the placement of Membrana tympanica, only the ventral part of the osseous concavity is tympanic cavity proper; the caudodorsal part is Meatus acusticus externus (Freund, 1926). See Annot. 19.

(22) Recessus columellae (new term). [Recessus antevestibularis] (NAA, 1979); Synonymy: Antivestibulum (Magnus, 1870); Recessus cavi tympani (Hasse, 1871); Recessus stapedialis (Stresemann, 1934). "Recessus columellae" replaces Recessus antevestibularis which is retained as an alternative. "Recessus columellae" is a more descriptive memory aid since this evagination of the tympanic cavity houses the basal portion of the ear ossicle (Columella) (Fig. 4.3) in the complex of otic bones. Fenestra vestibuli, Fenestra cochleae, and Recessus tympanicus caudalis open into the recess of the columella (see Annot. 26); the recess is lacking in certain birds, e.g., diomedeids, Mesozoic birds (Witmer, 1990); shallow in Latus, but relatively deep in others (e.g., Gallinula, Gallus, Strix, Ceryle).

Fenestra cochleae [F. pseudorotunda]. Synonymy: Fenestra rotunda. Opening within Os opisthoticum (Fig. 4.3), closed in life by Membrana tympanica secundaria. The avian and mammalian fenestrae are considered nonhomologous (de Beer, 1937); hence the term Fenestra pseudorotunda. Fenestra vestibuli. Synonymy: Fenestra ovalis. This opening into the vestibule of the osseous labyrinth is occupied by the footplate (base) of the Columella (see Sens. Fig. 16.7).

(23) Recessus pneumatici paratympanici (Resp. Annot. 21). Collective term for the three major, consistently occurring, air fllied evaginations of the tympanic cavity into the surrounding bones; namely, the rostral, caudal, and dorsal tympanic recesses. The openings or ostia by which the sinuses communicate with the tympanic cavity are called Foramina pneumatica (see Witmer, 1990). Among the several putative functions of the pneumatization of the skull of birds, Warnke 'and Stork (1977) suggest thermoregulation and insulation,

(24) Pila otica (new term). Synonymy: opisthotic columella (Lowe, 1926); Pila prootica (NAA, 1979). This usually short pillar of bone articulates with the quadrate bone (see below); since it ossifies with varying contributions from the opisthotic and prootic bones, its name has been simplified to Pila otica. The pila intervenes between the foramen of the dorsal tympanic recess and Recessus columellae (Fig. 4.3; Annot. 22).

Cotyla quadratica otici. Cup-shaped surface of the otic complex for articulation with the otic capitulum of the quadrate bone (Fig. 4.3). The cotyla is largely prootic in most birds with some contribution from the opisthotic. In some birds, the cotyla is partly located on the free end of the Pila otica. See paragraph above and Annot. 100.

(25) Recessus tympanicus dorsalis (Resp. Annot. 21). Synonymy: Recessus tympanicus superior (Suschkin, 1899; Pycraft, 1902;, Miiller, 1963); Antrum pneumaticum dorsale (NAA, 1979). The Foramen pneumaticum dorsale leading to the dorsal tympanic recess is located near the squamosal and otic articular facets for the quadrate bone (Fig. 4.3). Diverticula from this recess invade the prootic, squamosal, parietal and occipital bones.

(26a) Recessus tympanicus rostralis (Resp. Annot. 21). Synonymy: Recessus tympanicus anterior (Parker, 1869; Suschkin, 1899; Pycraft, 1902; Miiller, 1963); presphenoid sinus (Saiff, 1974); Antrum pneumaticum rostrale (NAA, 1979). Foramen pneumaticum rostrale of the rostral recess is located in the rostroventral part of the tympanic cavity, dorsal to the ostium of the auditory tube, and dorsolateral to the bony Canalis caroticus cranialis (see Figs. 4.2, 3, 5; Annot. 99). Diverticula from this recess invade the base of the skull (parasphenoid bone).

(26b) Recessus tympanicus caudalis. (Resp. Annot. 21) Synonymy: Recessus tympanicus inferior (Miiller, 1963); Antrum pneumaticum caudale (NAA, 1979). The Foramen pneumaticum caudale connects this recess with the columellar recess or the caudal part of the tympanic cavity. The Recess is ventrolateral to the rostral semicircular canal, and sends diverticula into the exoccipital bone.

(27) Canalis ophthalmicus externus. Synonymy: Canalis facialis; Canalis stapedialis. The canal conducts the A. et V. ophthalmica externa, and in some forms, the Chorda tympani of N. facialis. The caudal ostium of the canal is located in the Fossa parabasalis on the external skull base (Figs. 4, 5). The canal arches dorsal to the Columella then rostrally; its lateral wall may project in relief into the tympanic cavity, or may be incompletely ossified so that the lumen of the canal is visible in the dried skull. The rostral opening of the canal is medial to the otic process of the quadrate, lateral to Foramen n. maxillomandibularis.

(28) Basis cranii externa. Synonymy: basicranium. In this work "Basis cranii externa" is defined as limited to the exterior aspect of the bones forming the floor of the cranial cavity proper; thus Basis interna and externa of the cranium are opposites that correspond in area to one another. In some birds the cerebral surface of the base of the cranium is widely separated from the external surface by pneumatic spaces, evaginations of the tympanic cavity.

(29) Orbita. The osseous orbit of birds is bounded mainly by cranial bones. In most birds the floor of the orbit is not bone, but consists mainly of jaw muscles. Exceptions are the snipes and Woodcocks (Scolapacidae) in which the orbit is almost completely enclosed by bone (Hofer, 1955). See Annot. 30. Fonticuli interorbitales; Fonticuli orbitocraniales. Synonymy: Fonticuli orbitales, Barkow (1856); Foramina obturata orbitalia. In the dried skull these are unpaired deficiencies in the bone of the interorbital septum or paired ones in the caudal wall of the orbit; the latter communicate with the cranial cavity (Figs. 2, 3, 6). In intact specimens the fonticuli are closed by fibrous membranes.

(30a) Proc. postorbitalis. Synonymy: Proc. orbital is posterior; Proc. postfrontalis. In most carinate birds, and the ratite Rhea, the postorbital process is formed largely by Os laterosphenoidale; Os squamosal (e.g., some galliforms) or Os frontale (Struthio) contribute to the base of the Proc. postorbitalis. Consult Miiller (1963: 81) for discussion of the postorbital process. The postorbital process commonly forms the caudoventral border of the orbit (Figs. 4.2, 5); however, in certain birds (e.g., anseriforms) it projects rostrally and contributes to the ventral margin of the orbit (see below, Arcus suborbitalis). The tips of Proc. postorbitalis and Proc. zygomaticus are joined in some birds (e.g., psittaciforms and galliforms). See below and Annot. 108.

(30b) Arcus suborbitalis (Portmann, 1950). A complete osseous arch bounds the orbii ventrally in some psittaciforms, scolopacids (Gadow and Selenka, 1891), and the anatid, Dendrocygna (Shufeldt, 1909). This arch is formed by junction of a lengthy caudal extension of Os lacrimale and the rostral extension of the Proc. postorbitalis or the postorbital/zygomatic complex; in other birds these structures form an arch connected by Lig. suborbitale (Arthr. Annot. 30).

(31) Foramen orbitonasale laterale/mediale. Longitudinal opening(s) between the orbital surface of Os frontale and the dorsal border of Os ectethmoidale. A single slitlike foramen is present in some birds (e. g., Ardea, Aythya); both medial and lateral foramina are found in other birds (e.g., Columba, Gallus, Coragyps, Corvus.) The medial foramen (Fig. 4.1) conducts N. olfactorius and the medial ramus of N. ophthalmicus from orbit to nasal cavity; the lateral foramen conducts the lateral ramus of N. ophthalmicus and duct(s) of Glandula nasalis. Sulcus n. olfactorii. Longitudinal groove for the olfactory nerve and ethmoid artery; located in the angle between the upper part of the interorbital septum and the Lainina dorsalis of Os mesethmoidalis which is applied to the roof of the orbit (see Fig. 4, 1; Annot. 108).

(32) Foramen opticum. Located in the boundary zone between the caudal edge of the interorbital septum and the caudal wall of the orbit (Figs. ~, 2, 3). The foramen. In carinates is usually a single opening inside the cranial cavity, but the foramen is divided by the relatively thin interorbital septum into a pair of closely related foramina, one in each orbit. In some psittaciforms (pers. obs.) and carduelene finches(Zusi, 1978) the two optic foramina are widely separated from one another by a thick septum. In other birds the optic foramina may be continuous with the Fonticuli orbltocraniales and other foramina (Annot. 29, 88).

(33) Septum osseum fossae ·bulbi. The fossa for the olfactory bulb is divided by a bony septum in Apteryx (Starck, 1955) and in the albatross (Diomedea sp.) and psittacids.

(34) Foramen ethmoidale. Transmits A. et V. ethmoidalis into the orbit from the cranial cavity; separate openings for the artery and vein are present in some birds. See Annot. 31.

(35) Fossa cranii media. Synonymy: Fossa mesencephalica. The middle cranial fossa houses the Diencephalon and Chiasma opticum medially and the Tectum mesencephali on each side. The Fossa is not homologous with the middle cranial fossa of mammals. See Os basisphenoidale and Os laterosphenoidale for additional terms.

(36) Crista marginalis. This crest separates each side of the Fossa cerebelli from the general chamber of the vault of the calvaria that houses the telencephalic herruspheres of the brain.

(37) Tuberculum pineale. On the internal surface of the Calvaria the Tuberculum pineale is a triangular eminence at the junction of Crista frontalis interna with the marginal crests of the cerebellar fossa. The dorsal expanded end of the body of Glandula pinealis is closely related to the Tuberculum.

(38) Fossa auriculae cerebelli. Synonymy: Fovea hemispherii cerebelli; Fossa subarcuata. The fossa in birds contains the cerebellar auricle (Fig. 4, 6). "Subarcuate fossa" is inappropriate, since in mammals it lodges the endolymphatic sac; therefore the avian and mammalian fossae are non-homologous. See Ven. Annot. 35.

(39) Fovea ganglii vagoglossopharyngealis. In the floor of the caudal fossa of the cranium, the fovea (pit) is located in the suture between the exoccipital and opisthotic bones; the fovea houses the combined proximal [root] ganglia of the X and IX cranial nerves (Fig. 4.6). Separate foramina for each nerve are found in the bottom of the fovea that lead to the parabasal fossa on the external skull base (Figs. 4.4, 5). See Annot. 86; and PNS.

(40) Rostrum [Symphysis] mandibulae (new term). (Rostrum, L. beak or prow). The rostrum is the pointed, atypical region of the mandible formed by the union of the symphysial segments of the right and left mandibular rami. Although this region of ankylosis of the mandibular rami is commonly called the "mandibular symphysis", in the strict sense, the symphysis is the actual joint connecting the two. See Annot. 42; Arthr. Annot. 21. and Topog. Annot. 12.

Rostrum maxillae (new term, R. Zusi, pers. comm.). This is the pointed, apical region of the upper jaw formed by the ankylosis of the bodies of right and left premaxillary bones that corresponds to the Rostrum mandibulae (Fig. 4.2). See Topog. Annot 12.

(41) Foveae corpusculorum nervosorum. In the bones of the maxilla and mandible these small pits .deep to the rhamphotheca house sensory corpuscles (Fig. 4.2); the foveae are especialy numerous and conspicuous in the rostra of the upper and lower Jaw of Apteryx, ibisS and spoonbills, anseriforms, and sandpipers and snipes (Scolopacidae). See Annot. 57 and Sens. Annot. 66.

(42) Pars symphysialis/intermedia/caudalis (Lebedinsky, 1920). The symphysial part of the mandibular ramus is the rostral segment that unites with the opposite ramus at the Symphysis mandibularis (see Annot. 40 and Arthr. Annot. 21 and Fig. 4.4). Pars intermedia extends caudally to Zona flexoria intramandibularis caudalis which is often marked by the Fenestra rostralis mandibulae. Pars caudalis extends from the caudal flexion zone to the retroarticular process, and includes the area of attachment of the jaw muscles, facets for articulation with Os quadratum, and Fenestra caudalls mandlbulae in birds that have dual fenestrae on each side (Annot. 46). See Arthr. Annot. 46-48. The Ramus mandibulae is peculiar in caprimulgids in that the rostral attenuated one-third is set off by an oblique, moveable syndesmotic joint from the bowed stronger rear two-thirds. 

(43) Angulus mandibulae. This is the point on the dorsal border of the Ramus mandibulae  where the ramus becomes angulated or curved ventrally (e.g., charadriiforms, caprimulgiforms, columbiforms, falconiforms, and passerines). See Annot.56. The angle marks the caudal extent of the rhamphothecal sheath covering the exposed part of the mandible.

(44) Proc. coronoideus. Synonymy: Proc. pseudocoronoideus; Proc. m. adductoris mandlbulae. Any process of Pars caudalis of the mandible to which is attached the strong "aponeurosis" of M. adductor mandibulae externus, pars rostralis (Myol. Annot. 18). In different birds it is commonly found on the dorsal margin of the mandible, often coincident with the Angulus mandibulae (Johnson, 1984); it may, however, be located on the lateral surface of the mandible as in anseriforms (Zweers 1974). See Figs. 4.1,2. In finches, processes for the insertion of aponeuroses of M. adductor mandibulae externus "profundus" also occur caudal to Proc. coronoideus (Richards and Bock 1973) (see Myol. Annot. 18).

(45) Tuberculum pseudotemporale. Synonymy: Proc. pseudotemporalis. The pseudotemporal tubercle which is located slightly rostral to the quadratomandibular joint near the base of Proc. medialis mandibulae (Fig. 4.1) is the point of insertion of the tendon of M. pseudotemporalis superficialis (Myol. Annot. 19). The tubercle is prominent in heavy-billed finches.

(46) Fenestrae mandibulae. Synonymy: Foramen mandibulare anterior; Foramen mandibulare posterior (Lebedinsky, 1920); Foramen ovale; interangular vacuity or fenestra (Shufeldt, 1909). Fenestra rostralis mandibulae is found in the region of the caudal intramandibular flexion zone (Arthr. Fig. 2); Fenestra caudalis mandibulae occurs in Pars caudal is of the mandibular ramus (see Annot. 42, 48). The fenestrae may be completely lacking in some taxa. Other birds may possess only one of the fenestrae (e.g., Columba). Two fenestrae occur in certain birds (e.g., some charadriiforms, gruiforms, psittaciforms, and strigiforms). Consult Lebedinsky (1920) for details.

(47) Canalis neurovascularis mandibulae. Synonymy: The canal conducts vessels and the intramandibular ramus of the mandibular nerve from the region of the coronoid process to the symphysial region of Ramus mandibulae. See Annot. 48.

(48) Fossa aditus canalis neurovascularis. Synonymy: Fossa medialis mandibulae (Johnson, 1984). Depression on the internal aspect of Pars caudal is of the mandibular ramus that leads to the aditus or opening of the mandibular canal. The floor of the fossa often consists of thin bone. and may exhibit an opening(s), Fenestra caudalis mandibulae. The fossa is pronounced and extensive in many birds (e.g., Pygoscelis,Gavia, Cathartes, Anser).

Fossa lateralis mandibulae (Johnson, 1984). Shallow depression on the lateral aspect of the mandibular ramus at or near its rostral fenestra, e.g., Diomedea, Larus.

(49a) Fossa articularis quadratica. Area of the mandible for articulation with the condyles of Proc. mandibularis of Os quadratum (see Fig. 4.3; Annot. 72). Cotylae fossae articularis. These are the facets for articulation with the condyles of the Os quadratum. The medial cotyla is separated from the others (see below); however, the lateral and caudal cotylae are merged into a common articular surface in some birds (e.g., Larus); distinct in others (e.g., Ardea, Morus). Sulcus intercotylaris; Thberculum intercotylare (Johnson, 1984); [Crista intercotylarisl (Zusi, 1987). The groove, boss of bone, or bony crest in the articular fossa of the mandible of different birds; these structures separate the medial and lateral cotylae (Fig. 4.3). The tuberculum is especially prominent in psittacids.

(49b) Proc. retroarticularis. Synonymy: Proc. mandibularis posterior (Lebedinsky, 1920); Proc.angularis posterior (Hofer, 1945); postarticular process. This process projects caudally past the articular fossa of the mandible; formed mainly by the Os angulare to the rear of Proc. lateralis mandibulae. Weakly developed, pointed, or stubby in most birds, the retroarticular process is prominent, e.g., in galliforms, ciconiiforms, psittaciforms, anseriforms and phoenicopterids (Arthr. Fig. 5.20); in the last two taxa the process is attenuated and blade-like. The Proc. retroarticularis is also well developed in birds that forcefully open the jaws while foraging, probing into flowers or fruit (Zusi, 1967). Well developed in Aechmophorus, but not in other grebes CR. W. Storer, pers. comm.). See Annot. 50, 51.

Incisura retroarticularis (Johnson, 1984). In lateral view of the caudal segment of the mandibular ramus, this is a notch between the Proc. lateralis mandibulae and the retroarticulair process; the incisure is the notched edge of the lateral cotyla.

(49c) Foramen pneumaticum articulare. An opening in the upper surface of Proc. medialis maridibulae (formed by Os articulare) that leads to pneumatic spaces in the caudal segment of the mandibular ramus (Figs. 4.1, 3); the lower jaw of some birds is extensively pneumatic (e.g., flamingos, hornbills, toucans). The Siphonium is a connective tissue tube, ossified in some birds (e.g., Corvus), that connects the pneumatic foramen of Os articulare with the mandibular diverticulum of the tympanic cavity. See Cavum tympanicum; and Witmer (1990).

(49d) Proc. medialis/lateralis mandibulae. Both of these are processes of Pars caudalis of the mandible (mainly Os articulare); Proc. medialis mandibulae (Figs. 4.1, 3) is much the stronger of the two; it projects medially with its tip curved dorsally (exception: psittaciforms)(see below). The weak lateral process forms part of the cotyla for the lateral condyle of the quadrate bone; in some birds it is the attachment of Lig. postorbitaie (Arthr. Annot. 42). See also Arthr. Annot. 32.

Facies articularis parasphenoidalis. In certain birds this articular surface near the tip of the Proc. medialis mandibulae forms a joint with the lateral or medial parasphenoidal process of Lamina parasphenoidalis of the external base of the skull (see Annot. 96 and Arthr. Annot. 32).

(50) Recessus conicalis. Synonymy: Fossa conicalis (Shufeldt, 1909). Recessus posterior (Lebedinsky, 1920); Cavum mandibulare (Zweers, 1974). In anseriform birds this is an unusual, deep recess ventral to the medial cotyla of the quadratomandibular joint. Its opening is located between the blade-like Proc. retroarticularis and Proc. medialis mandibulae. A somewhat similar deep recess is present in certain psittaciforms, however its opening faces dorsally rather than caudally. See Annot. 51.

(51) Fossa caudalis. Synonymy: Fossa posterior (Lebidinsky, 1920); postarticular surface (Milne-Edwards, 1867-71). In birds of many different taxa this term refers to the shallow concavity of the caudal surface of Proc. mandibulae medialis, located medial to the retroarticular process (Fig. 4.1). This is the area for insertion of M. depressor mandibulae (Myol. Annot. 24); (Arthr. Annot. 37). See Lebidinsky (1920) for a detailed, comparative account of Fossa caudalis in numerous avian taxa.

Crista transversa fossae (new term). This distinct transverse crest extends from the Proc. medialis mandibulae to Proc. lateralis mandibulae Fig. 4.3). The crest separates two different fossae; it forms the caudal wall of the articular fossa for Os quadratum, and its rear surface is the upper part of Fossa caudalis (see above). The crest, which exhibits a distinct tubercle in some birds, is an attachment of Membrana postmeatica and Lig. occipitomandibulare. See Arthr. Annot. 37.

(52) Ossa mandibulae. Each ramus of the mandible is considered to consist of seven separate bones. Different names for the various elements abound in the literature. The tabular synonymy compiled by Miiller (1963) is summarized below; terms selected by him are followed in this present terminology with one exception. Os coronoideum is not ordinarily present in birds.

Os dentale. Synonymy: dentary; dentosplenial; mentomandibulare. This is the principal element of each mandibular ramus (Fig. 4.1); it articulates with the supraangular and splenial elements by squamous sutures at the junction of intermediate and caudal segments of the ramus. Os articulare forms most of Fossa articularis quadratica. See Lebedinsky (1920) and Jollie (1957) dealing with the mandible of carinates, and Miiller (1963) regarding the ratite mandible.

Os prearticulare. Synonymy: Os goniale; Os coronoideum, Synonymy: Os complementare; Os spleniale, Synonymy: Os operculare; Os supra-angulare, Synonymy: surangulare. Os mentomandibulare. According to Romonoff (1960:995) paired mentomandibular elements replace the cartilage at the mandibular symphysIs, then ankylose with one another.

(53) Os maxillare;  Maxilla. As an individual bone, Os maxillare is one of the components of the avian upper jaw. As a general term, "Maxilla" refers to the entire complex of structures that make up the upper jaw; i.e., the opposite of "Mandibula", the lower jaw (see Annot. 40 and Topog. Annot. 8).

(54) Proc. maxillaris Synonymy: Proc. postnarialis or P. subnarialis. Proc. premaxillaris. Synonymy: Proc. dorsonarialis. Process of the nasal bone.

(55) Septum nasi [nasale] osseum; Conchae nasales. These structures may be supported in part by the vomer, maxilla, and ectethmoid bones. The rostral part of the nasal septum and nasal conchae in the caudal part of the nasal cavity vary in the extent that they ossify in different birds, usually remaining more or less cartilaginous. These structures characteristically ossify extensively in, for example, Diomedea, some parrots, birds of prey (Buteo, Strix), herons and ibis (Ardea, Eudocimus), pelecaniforms, trochilids, Coccyzis, some coraciiforms, and passeriforms. See Annot. 10; Resp. Annot. 6-9.

(56) Crista tomialis. Synonymy: tomial shelf (Johnson, 1984). The paired sharp edges of the upper and lower jaws (Figs. 4.2, 4). Hard keratinized rhamphotheca invests the crests from the tips of the rostra of mandible and maxilla caudally to the level of the Angulus mandibulae. See Annot. 43, 44; Integ.

(57) Canalis neurovascularis maxillae. Paired longitudinal canal that conducts the tenninal branch of N. ophthalmicus and accompanying vessels from the rostral end of the nasal cavity into the Rostrum maxillae (Annot. 40) of the upper jaw (mainly in Os premaxillae). The canal is relatively long, e.g., in a heron or duck, quite short in a gull or vulture. In birds with large maxillary bones (e.g., Anas, Anser, Larus, and Hesperornis) a separate neurovascular canal enters the maxilla near its junction with the jugal arch; this canal conducts parts of the nasopalatine branch of N. maxillaris to openings on both medial and lateral sides of the caudolateral maxillary tomial crest and adjacent palate (see below). 

Foramina [Pori] neurovascularia. The ramifications of the branches of the ophthalmic and nasopalatine nerves (and companion vessels) leave their neurovascular canals (Fig. 4.2) via smaller Canaliculi neurovasculares that open on the surface of the bone of the upper jaw via foramina (pores) deep to the rhamphotheca (especially in the Rostrum maxillae). The foramina often open into Foveae corpusculorum nervorsorum, pits or hollows beneath the rhamphotheca which house sensory corpuscles; the foveae are remarkably abundant in Capella. See Annot. 41; and Sens. Annot. 70.

(58) Proc. maxillopalatinus [Proc. palatinus]. This process of Os maxillare in many birds arises from the maxilla near its junction with Proc. maxillaris of Os palatinum (Figs. 4.1, 4; Annot. 64). The maxillopalatine process of different birds exhibits a variety of orientations and configurations largely due to variation in the form of the maxillary diverticulum of the antorbital sinus (Witmer, 1990); it contributes to the formation of the nasal cavity in most birds and to the palate in the birds such as anseriforms, ciconiiforms, and passeriforms (see Hofer, 1949). In anseriforms the right and left maxillopalatines are synostosed in the median plane.

(59) Proc. jugalis. This process of Os maxillare has also been called Proc. labialis (see Annot. 11).

(60) Os palatinum [Os pterygopalatinum] (see Annot. 61 and Fig. 4.4, 7). Four features of the palatine bone are common to most birds: Pars choanalis which is associated with the Fossa choanalis (see below, this annot.); (2) Pars lateralis (see next paragraph) which is generally lateral to Pars choanalis, is associated mainly with the attachment of M. pterygoideus; (3) Proc. maxillaris (synonymy: Proc. premaxillaris, NAA, 1979; prepalatine, Parker, 1879), connected to the maxilla, is usually a slender bar which, in all neognathines, has a bending zone (Zona flexoria palatina, see Arthr.); (4) Proc. pterygoideus (synonymy: postpalatine, Parker, 1879) connects the palatine with the pterygoid bone, and may include a fused portion of Os pterygoideus (see Annot. 61). Certain features listed under Pars choanalis and Pars lateralis are absent in some birds; Parker (1879), Hofer (1945), and Richards and Bock (1979) discuss the variety of shapes and relationships of palatine bones in different avian taxa, and include other palatine features not presented in this terminology. Ziswiler (1985) provides a concise summary on types of avian palates; see Witmer and Martin (1987) for a critique of palatal typology.

Pars lateralis (Fig. 4.7) in part replaces the term "Lamella caudolateralis" of the NAA (1979), a term derived from Proc. posterolateralis of (Beddard, 1898; Hofer, 1945; and Biihler, 1970); Lamella caudolateralis is retained as an alternative (bracketed) term in the present edition. Pars lateralis is usually a flared plate facing ventrally in some birds, obliquely ventromedially in others, and medially as in psittacids (Beddard, 1898). Pars lateralis is convoluted in Fulica, and extremely expanded laterally in caprimulgids.

Fossa choanalis (Fig. 4.7). Synonymy: Fossa medialis (NAA, 1979). Paired, shallow furrow between the medial and ventral crests of Pars choanalis of Os palatinum (Fig. 4.4); the furrow faces medially, fonning the laterai wall of the chamber of the Choana which connects nasal cavity with oropharynx (see Annot. 64; and Resp.Annot.5).

(61) Os pterygoideum (Figs. 4.4, 2, 5). Pars palatina of Os pterygoideum that joins Os palatinum (Annot. 60) is also known as the antero-, hemi-, or mesopterygoid (Parker, 1879; Pycraft, 1900; Jollie, 1957). Biihler, et al. (1988) indicate that most modem prokinetic neognathines have this palatal ontogeny wherein an "intrapterygoid" joint forms between Pars palatina and the rest of the pterygoid bone from which it was detached in early postnatal life (see Arthr. Annot. 17). In paleognathine birds and some neognaths, no part of the pterygoid splits off (Jollie, 1957). According to Hofer (1945) Os pterygoideum may be arched (e.g., Mergus), bent (e.g., Vanellus), or extended (e.g., Ardea). See Annots. 69, 70, 93.

(62) Facies articularis parasphenoidalis. The surface at the zone of contact between the palatine bone and parasphenoid rostrum. Such contact and articulation are absent in some birds. In some passerines and a few other taxa, a winglike portion of the parasphenoid facies, the Lamella dorsalis (synonymy: palatine hasp, Richards and Bock, 1973), extends up alongside the lateral surface of the rostrum; the edge of Lamella dorsalis is Crista dorsolateralis (synonymy: Cr. dorsalis, NAA, 1979).

Crista medialis (Fig. 4.7). This is the medial edge of the border of the surface of Pars choanalis that articulates with the Rostrum parasphenoidale. In some birds the right and left medial crests fuse in the midline on the lower surface of the parasphenoid rostrum and exhibit an unpaired median crest (most pelecaniforms, Capella, Steatomis, Podargus).

(63) Proc. rostralis (Jollie, 1958). Synonymy: Proc. choanalis rostralis (Biihler, 1970; NAA, 1979); ethmo-palatine bar (Parker, 1879). This is a rostral extension of the Crista medialis or Lamella dorsalis of Pars choanalis of the palatine bone for articulation with the Vomer; well exemplified in Anser, Ardea, Caprimulgus, Corvus).

(64) Lamella choanalis (Fig. 4.7). Synonymy: wall of palatine trough (Richards and Bock, 1973). A curved plate, often deeply concave, of Pars choanalis forming the lateral and dorsal wall of the Fossa choanalis of each palatine bone. In caprimulgids, the dorsal part of the lamella is curved medially and fused with its counterpart in the midline ventral to the parasphenoid rostrum, forming a palatine roof of the Pars caudal is of the choana (see Resp. Annot. 5). In some birds the plate is extended vertically ventrally forming the Crista ventralis which deepens the caudal part of the choana, pronounced, e.g., in Larus and Diomedea. In birds whose palatines are apposed or fused in the median plane, the right and left Cristae ventrales together form an unpaired, median ventral palatine crest (e.g., Morus). Angulus caudomedialis. The angle formed by the caudal border of Lamella choanalis with its Crista ventralis. Proc. caudomedialis. Synonymy: mediopalatine process (Richards and Bock, 1973). A caudal projection of Crista ventralis of some birds.

(65) Crista lateralis. The thickened lateral edge of the Pars lateralis of the palatine bone to which the aponeurosis of M. pterygoideus is attached.

(66) Angulus caudolateralis. Angle at the intersection of caudal and lateral margins of Pars lateral is of the palatine bone. In some forms (some passerines and a few other taxa) the angle is prolonged caudally as a pointed process which has been called the "transpalatine process", not an apt descriptive term.

(67) Fossa ventralis. Synonymy: Fossa muscularis. A usually shallow excavation on the ventral surface of Pars lateral is of the palatine bone between its Crista lateralis and Crista ventralis for attachment of part of M. pterygoideus. The fossa is deep in birds with prominent ventral crests of, e.g., Diomedea, Cathanes, Larus, Capella.

(68) Vomer. Synonymy: Prevomer. Paired elements, in adults most .often fused into a single median structure that typically articulates with the parasphenoid rostrum and/or the Pars choanalis of the palatine bone (see below, this paragraph); not present in all birds; weakly developed in galliforms. The (fused) vomer varies in shape, ranging from a horizontally flanened plate, strongly V-shaped in cross section, to a laterally compressed, vertical plate. In passerine birds the vomer extends into the "ethmoid tissue" (Fig. 4.4), a condition unique to this group (see Hofer, 1949). In palaeognaths the vomer and pterygoids exclude the paired palatines from contact with one another and with the parasphenoid rostrum. In paleognaths the vomer has articular surfaces for pterygoid, palatine, maxillary, and premaxillary bones in addition to the Rostrum parasphenoidale.

(69) Facies articularis parasphenoidalis. In many neognathine birds the pterygoid, palatine bones, and the Vomer have surfaces for articulation with Rostrum parasphenoidale (Arthr. Annot. 29, 15, 16, 23).

Pes pterygoidei (Johnson, 1984). The "foot of the pterygoid", i.e., the expanded rostral end of the pterygoid bone (Fig. 4.4) that has articular surfaces for the parasphenoid rostrum and the palatine bone.

(70) Proc. dorsalis. Dorsal muscular process of Os pterygoideum of many birds, especially prominent in woodpeckers (Picidae) (Hofer, 1945). See Myol. Annot. 21.

(71) Os quadratum. Synonymy: Quadratum. Walker (1888) presented a comparative description (1888) of the variable form of the avian quadrate bone. Proc. oticus of the quadrate articulates with the prootic/opisthotic and squamosal (and sometimes laterosphenoid) elements by means of often separate otic and squamosal capitula. In some birds (e.g., Hesperornis, ratites, some neognaths; Witmer, 1990) the Incisura intercapitularis is indistinct and the capitula merge, lending the appearance of being "single-headed". See Annot. 24, 100; and Figs. 4.2, 3, 5).

Facies tympanica. The tympanic surface of the otic process and upper body of the quadrate bone forms with Ala parasphenoidea the rostral wall of the tympanic cavity; the tympanic membrane is attached to the crest of this surface. See Annot. 19.

(72) Condylus caudalis. Synonymy: Proc. postmandibularis. The Proc. mandibularis of the quadrate bone of most taxa of birds possess three condyles (see Bock, 1960; and Arthr. Annot. 35). The three condyles are arranged in a somewhat triangular configuration, the caudal condyle projecting toward the rear. '

Condylus pterygoideus. In most birds the condyle of Os quadratum for articulation with the lateral end of Os pterygoideum has a rounded, convex articular facet (Fig. 4.3). In ratites, tinamous, and the hesperornithiforms the facet is broad and flattened (Witmer, 1990).

Condylus lateralis. In most birds the lateral condyle of the quadrate bears only the articular facet on its ventral surface for the Cotyla lateralis of the mandible (Fig. 4.5); however, most endemic New World jays (e.g., Aphelocoma) possess an additional condyle (Condylus rostralis) on the rostral surface of the lateral condyle of the quadrate. This condyle fits into a caudally-facing Cotyla rostralis on the mandible directly above the lateral cotyla. This forms the "buttress complex" (Zusi, 1987), anchoring the mandible to the quadrate when the open lower jaw is used in pounding.

(73) Cotyla quadratojugalis. The cotyla of the quadrate bone for articulation with the Condylus quadraticus of Os quadratojugale is located on the root of the lateral condyle of the mandibular process of Os quadratum.

(74) Ossa supraorbitalia (Beddard, 1898). Synonymy: Os supraciliare.

(75) Ossa accessoria cranii. See Jollie (1957) for a discussion of the accessory bones of the avian head.

(76) Os nuchale. Synonymy: Stylus postoccipitalis. Apparently unique to cormorants (Phalacrocorax) and the Anhinga in which it forms a moveable joint with a rounded protuberance of the occipital region of the skull (Dullemeijer, 1951).

(77) Anulus [Annulus] tympanicus. An osseous ring to which the periphery of the tympanic membrane is attached occurs in strigiforms and Gallus (Stellbogen, 1930). The ring is formed by parts of the exoccipital and parasphenoid bones (Kiihne and Lewis, 1985).

(78) Ossa suturarum. Supernumerary bones developed in sutures between cranial bones; seen readily in young turkeys and ducks.

Os uncinatum (Burton, 1970). Located between the ventral end of Os lacrimale and the jugal bar in examples of musophagids.

(79) Apparatus hyobranchialis (Goodrich, 1958). Synonymy: Apparatus hyolingualis (consult Myol. Annot. 25); Apparatus hyoideus. The avian "tongue skeleton" is made up principally of elements from the hyoid arch and other more caudal branchial arches. The terminology adopted is that of McLelland (1968). Miiller (1963:56) provides a comprehensive synonymy. Zweers (1974, 1982) described the hyobranchial apparatus in Anas and Columba; he noted that the hyobranchial elements are commonly cartilage rather than bone.

(80) Paraglossum. Synonymy: Entoglossum. The paraglossum of most birds has the shape of an arrow head, bearing short, caudolaterally directed cornua. Psittaciforms possess a wide, flat paraglossum with a central foramen, or, more commonly, paired paraglossals united rostra11y by a carti1aginous or bony isthmus (Beddard, 1898). In Psittacus (Hornberger, 1986) each of the paired paraglossals is bifurcate rostrally.

(81) Basihyale. Synonymy: Basibranchiale rostrale; Basihyoideum; Pars basihyalis copulae; Copula I (Muller, 1963). This element is a derivative of the hyoid arch. See below.

Proc. parahyalis; Arcus parahyalis. In parrots (Mivart, 1895; Homberger, 1986) the Basihyale possesses a caudal enlargement from which the dorsolateral Proc. parahyalis arises on each side. These processes unite mid-dorsally to form the paraglossal arch in several Australian and Indopacific genera (Melopsittacus, Eos, Vini, Lorius, and Nestor).

Urohyale. [Basibranchiale caudale]; Synonymy: Urohyoideum; Pars urohyalis copulae; Basibranchiale 1; copula II (Muller, 1963). The Basihyale and Urohyale are separate in young birds, but fused to one another in adults.

(82) Dentes. True teeth are known only from the fossil birds Archaeopteryx, Parahesperomis. Hesperomis, and Ichthyomis (Gingerich, 1972; Martin, 1984). Martin, et aI. (1980) reviewed the morphology of avian dentitions. In Osteodontomis (Pseudodontornithidae) and its relatives the "teeth" are bony projections of the jaws, covered by rhamphotheca (Howard, 1957).

(83) Condylus occipitalis. The main part of the condyle is formed by Os basioccipitale; lateral contributions are from Os exoccipitale on each side. For a comprehensive comparative study of the avian occipital condyle see Goedbloed (1958).

Incisura mediana condyli. This is the median notch, usually present on the dorsum of the occipital condyle (Fig. 4.5); the tip of the Dens of the Axis rides in the incisure during dorsiflexion of the atlanto-occipital joint (Landolt and Zweers, 1985; Weisgram and Zweers, 1987). See Arthr. Annot. 64.

Tuberculum basilare. Synonymy: marnillary proc. (Pycraft, 1902; Saiff, 1974; Witmer, 1990). The basal tubercles originate as paired swellings at the rostral comers of the basioccipital bone; in later development they become sheathed ventrally by Lamina parasphenoidalis (Fig. 4.3). The tubercles serve for insertion of cervical muscles, principally M. rectus capitis dorsalis. They are best developed in long-skulled birds, e.g., Morus, Hesperomis. In some cases, the tubercles may coincide with Proc. medialis parasphenoidalis (see Annot. 97). Tuberculum basilare is an appropriate name in that it is clearly homologous with the "basal tubera" of nonavian archosaurs .

(84) Ala parasphenoidalis. Synonymy: Ala tympanica (NAA, 1979); alaparasphenoidalis (Jollie, 1957). Although this part appears to be a lateral extension of Lamina parasphenoidalis (Erdmann, 1940), it is actua1Jy formed as a separate center of ossification that merges with the lamina in certain birds, remaining separate in others (Figs. 4.4). In some birds the Ala parasphenoidalis is flared and wing-like, forming part of the margin of the external acoustic meatus (Annot. 20). In others the ala is not wing-like, but a boss of bone, the Proc. lateralis parasphenoidalis (Annot. 97) that  forms a joint with the Proc. medialis mandibulae (as in Diomedea, Morus, and Larus). See Arthr. Annot. 32.

(85) Proc. paroccipitalis (Shufeldt, 1909) [p. paroticus] (NAA, 1979). Synonymy: Ala posttympanica; Proc. occipitalis lateral is (Davids, 1952); Proc. opisthoticus (Zusi, 1962). Proc. exoccipitalis (Richards and Bock, 1973; Johnson, 1984). The paraoccipital process forms the caudal wall of Cavum tympanicum and Meatus acusticus, and provides attachment for Lig. occipitomandibularis (Arthr. Annot. 37) and M. depressor mandibulae (Figs. 4.4, 3, 5). The paroccipital processes of Mesozoic birds are directed more or less laterally (Witmer, 1990, whereas those of most neornithine birds project ventrolaterally. These processes are especially prominent in Gavia, Pelecanus, Anser, and Caprimulgus.

The paroccipital process is a compound bone formed by three elements: (1) the opisthotic medially; (2) the metotic laterally (see Annot. 105); and (3) the exoccipital which forms a caudal sheath of variable lateral extent.

(86) Fossa parabasalis (Kesteven, 1925). Synonymy: Fossa jugularis. Depression on the exterior of the skull base, just medial to the ventral margin of the tympanic cavity. Canals for cranial nerves VII, IX, X, (X), the cerebral carotid and the external ophthalmic arteries open into the fossa (Fig. 4.5). Not present in all birds.

Crista fossae parabasalis. This crest forms the prominent raised medial margin of the parabasal fossa as in examples of anseriforms and phoenicopterids (flamingos).

(87) Fonticulus occipitalis. Synonymy: Fonticulus occipitalis lateralis (Barkow, 1829); occipital fontanelle. Large paired openings lateral or dorsolateral to the Foramen magnum as in the anseriforms, some alcids, scolopacids, gruids and aramids, threskiornithids, and phoenicopterids (Beddard, 1898). These openings, like the orbital fonticuli (Annot. 29), are closed by fibrous membranes in intact specimens. Olson and Feduccia (1980) discuss the taxonomic significance of the fonticuli.

(88) Os laterosphenoidale [Os pleurosphenoidale]. Synonymy: Os orbitosphenoidale (NAA, 1979); Os alisphenoidale. This bone forms much of the ventral part of the caudal wall of the orbit, and extends from the interorbital septum (where it is notched or perforated for cranial nerves II, ill, IV, and VI) laterally to the temporal fossa and the postorbital process (see Annot. 30) and tympanic cavity; it forms part of the margin of Foramen n. maxillomandibularis (Lang, 1956). In addition to the large laterosphenoid ossification, there is often a separate late-appearing ossification, the orbitosphenoid, a dorsomedial element that fuses with its counterpart and the mesethmoid (Hogg, 1978; Goodrich, 1958; and Muller, 1963).

(89) Area muscularis aspera. The orbital surface of Os laterosphenoidale of many large birds exhibits a roughened area for attachment of the jaw muscles; extremely pronounced in Phoenicopterus (Myol. Annot. 19).

(90) Foramen n. maxillomandibularis. Synonymy: Foramen prooticum spurium (Miiller, 1963). Single opening between the prootic and laterosphenoid bones in birds and other archosaurs that transmits the N. maxillomandibularis (Figs. 4.1, 3, 6). Apparently only a small proportion of birds possesses separate foramina for the maxillary and mandibular nerves, e.g., Tyto, Buteo, Cathartes (Barnikol, 1953), Columba, some Gallus (pers. obs.).

Canalis n. maxillomandibularis. In some forms (e.g., Columba) the maxillomandibular nerve traverses a relatively lengty canal to exit the cranial cavity, whereas in others (e.g., Corvus) the opening is simply a hole in thin bone, a foramen.

Foramen n. ophthalmici. Synonymy: Foramen rami profundi V. This foramen is located between the laterosphenoid and the basisphenoid/parasphenoid/interorbital septum complex.

(91) Sella turcica; Dorsum sellae. Consult Jollie (1957) and Hogg (1978) for the development of the base of the skull in the chicken; Muller (1963) in Rhea. For the anatomy of the Sella turcica in different birds see Wingstrand (1951), Starck (1955), and Baumel (1968). The Sella houses the hypophysis. The rostral end of the cranial carotid canal is an opening in the rear wall of the Sella, the Dorsum sellae, which is completely osseous in some birds, fibrous in others (Baumel, 1968).

Foramen ophthalmicum internum. Conducts the internal ophthalmic vessels into the orbit from the Sella turcica.

(92) (Canalis craniopbaryngealis). This vestige of the embryonic Rathke's pouch may be seen in a median section of the skull base. The canal connects the Sella turcica to a median foramen on the Basis cranii exterma (Wingstrand, 1951; Muller, 1963; Witmer, 1990).

(93) Proc. basipterygoideus. Synonymy: Proc. pterygoideus. A process on each side of Rostrum parasphenoidale (see Annot. 96) for articulation with the pterygoid bone. Occurs in ratites, procellariiforms, anseriforms, and galliforms; many charadriiforms and cathartid vultures; some caprirnulgiforms and strigiforms; and trogoniforms (see Beddard, 1898). The homologies of the basipterygoids in extant birds, Cretaceous fossil birds, as well as non-avian archosaurs are discussed by Witmer and Martin (1987) and Olson and Feduccia (1980).

(94) Tuba auditiva [pbaryngotympanica) communis. In most birds, the common auditory tube or chamber is formed by the confluence of the right and left tubes (see Annot. 98 for exceptions). The common tube is located on the ventral aspect of the base of Rostrum parasphenoidale (Fig. 4.4) (Basis rostri paraspbenoidalis), where it is well delineated (e.g., in Anser). The common tube opens into the Infundibulum tubarum, a chamber which itself passes through a median slit in the roof of the oropharynx. See Annot. 98; and Digest. Annot. 19.

(95) Canalis orbitalis. This short canal opens on each side of the base of Rostrum parasphenoidale (Fig. 4.3); it is an offshoot of the cranial carotid canal that transmits the carotid branch, A. sphenoidea (Art. Annot. 18).

(96) Lamina paraspbenoidalis [L. basitemporalis]. Synonymy: basitemporal plate; Lamina basiparasphenoidalis (NAA, 1979). On the Basis cranii externa, this lamina is located rostral to the area where the ventral neck muscles insert on the basioccipital bone in front of the occipital condyle (Figs. 4.4, 5). The lamina assumes markedly different configurations in various birds (see Annot. 98), moreover, the lamina of certain birds exhibits processes (see below) that articulate with the medial process of the mandible, forming the so-called "mandibular brace" of Bock (1960). See Annot. 83 regarding Thberculum basilare and Arthr. Annot. 32.

"Basitemporal" is inappropriate since the Lamina is not related to a "temporal" bone (see synonymy of as squamosum) or region; it is retained as a bracketed alternative term because of its widespread use. "Lamina parasphenoidalis" is an abbreviated form that does not reflect its origin from the basiparasphenoid center of ossification.

Rostrum parasphenoidale [R. sphenoidale]. Synonymy: sphenoidal rostrum (Shufeldt, 1909; as rostroparasphenoidale). Attenuated prolongation of the Basis cranii externa to which the lower border of the interorbital septum is joined and with which the pterygoid and palatine bones articulate. See Figs. 4.6, 3, 5.

(97) Proc. lateralis parasphenoidalis; Proc. medialis parasphenoidalis. Synonymy: medial and lateral basitemporal processes (Bock, 1960). Bock has described these processes of the parasphenoid lamina in detail for representatives of numerous avian taxa; Kozlova (1961) described them in alcids. See Arthr. Annot. 32 for particulars; see also Annot. 83 concerning Thberculum basilare.

(98) Tuba auditiva [T. pharyngotympanica]. Synonymy: Eustachian tube. This paired osseous tube is lined with mucosa continuous with that of the tympanic cavity and the oropharynx. The tube parallels the usually oblique, rostrolateral border of Lamina parasphenoidalis (nearly transverse in Phoenicopterus). The tube extends from the tympanic cavity to the base of Rostrum parasphenoidale, and most often joins the opposite tube (Annot. 94). The rostral openings of the tubes in ratites and the Cretaceous hesperornithiforms (Witmer, 1990) are widely separated. In some birds (e.g., albatrosses, flamingos) the lateral osseous wall is lacking, completed by connective tissue (Saiff, 1974).

(99) Canalis caroticus cranialis. Synonymy: parabasal canal (Muller, 1963, p. 76); vidian or basipterygoid canal (Goodrich, 1930); carotid canal (Shufeldt, 1909:283). Here it is qualified as the "cranial carotid canal" to distinguish it from the cervical carotid canal (Annot. 121). The cranial carotid canal extends from the parabasal fossa through the skull base medial to the auditory tube, then into the Sella turcica (Annot. 91); not only does it conduct the carotid vessels, but branches of cranial nerve VII. See Wingstrand (1951), Jollie (1957), Muller (1963: 76); and Baumel (1968) for particulars.

(100) Cotyla quadratica squamosi. Cup-shaped surface of Os squamosum for articulation with the squamosal capitulum of the quadrate bone (see Fig. 4.3; Annot. 24, 103). In some birds (e.g., Anas) the laterosphenoid bone makes a substantial contribution to the squamosal coytyla.

(101) Fossa acustica interna. Located on the lateral wall of the caudal fossa of the cranial cavity near the fossa for the auricle of the cerebellum, this depression contains the exit foramina for the branches of the vestibulocochlear and facial nerves. See Ossa cranii for more terms.

(102) Os squamosum [Squamosum]. Synonymy: as temporale.

Proc. zygomaticus Synonymy: Proc. lateralis. This process of Os squamosum is situated ventral to the postorbital process and is strongly developed in some birds, e.g., ratites, gaviiforms, galliforms, piciforms, and passeriforms (Figs. 4.4, 5). The tip of Proc. zygomaticus is fused with the postorbital process in some birds (e.g., galliforms). See Annot. 30b.

(103) Proc. suprameaticus. This process of Os squamosum forms part of the cotyla for the squamosal capitulum of the quadrate bone; and contributes to the upper boundary of the external acoustic meatus.

(104) Fossa temporalis. Excavation on the lateral aspect of the cranium dorsal to the external acoustic meatus and caudal to the postorbital process (Figs. 4.1, 5). In some birds (e.g., larids and ardeids) the fossa is strongly etched into the cranium (mainly as squamosum). In some birds its sharp border, Crista temporalis nearly reaches the median plane dorsally (Fig. 4.5). A tough fibrous membrane invests the the jaw muscles occupying the fossa (Arthr. Annot. 31).

Fossa subtemporalis. In some birds (e.g., Morus, Gallus, Haematopus, Ardea, Fulica) this is a shallow concavity between the caudal margin of the temporal fossa and the lateral part of the transverse nuchal crest (Fig. 4.1; Annot. 17).

(105) Ossa otica. In early postnatal development the three major otic elements (Os prooticum, Os epioticum, Os opisthoticum) coalesce with one another and adjacent surrounding bones. This complex contains the osseous labyrinth of the inner ear (Sandoval, 1963; Hogg, 1978). Os metoticum is an additional element lateral to the auditory capsule and forms much of the paroccipital process (see Toerien, 1971; and Annot. 85). The metotic cartilage is a neomorph of embryonic birds, and perhaps other archosaurs, that attaches to the basal plate, occipital arch, and auditory capsule (de Beer and Barrington, 1934). See Cavum tympanicum.

(106) Crista vallecularis. Crest of bone on the inner aspect of the calvaria that marks the lateral border of the Eminentia sagittalis of the cerebrum (CNS Annot. 78). The crest occupies the longitudinal groove in the brain surface known as the Vallecula telencephali.

(107) Proc. lacrimalis [P. prefrontalis]. Lateral flared projection of the lateral margin of the frontal bone immediately caudal to its articulation with Os lacrimale; present, e.g., in Larus, Morus, Cathartes. See Annot. 110.

(108) Os mesethemoidale. This bone forms much of the rostral osseous part of the interorbital septum and, in some birds, part of the nasal septum (Fig. 4.1); it also forms the Lamina dorsalis (see below).

Lamina dorsalis (Shufeldt, 1909). The transverse plate of Os mesethmoidale that lies perpendicular to the interorbital septum. The Lamina articulates with the ventral surface of the frontal bone; prior to fusion of these two elements it is seen readily in skulls of young chickens and ducks (e.g., Aythya). In rhynchokinetic skulls the Lamina dorsalis extends rostrad to the level of the craniofacial flexion zone. See Arthr. Sut. front. eth.

(109) Os ectethmoidale. [Os laterOethnioidale]; Synonymy: Proc. or (Planum) antorbitalis(e); Aliethmoid and Pars plana (Shufeldt, 1909). Vertical, transverse plate of bone forming part of the rostral wall of the orbit, separating it from the nasal cavity (Figs. 4.1, 2). In certain birds the lacrimal is fused with the ectethmoid forming the lacrimal-ectethmoid complex (Cracraft, 1968), e.g., in some charadriiforms (Larus, Haematopus) (Johnson, 1984).

(110) Os lacrimale [Os prefrontale]. Muller (1963) reviewed the controversy over the homology of the lacrimal/prefrontal bone. Witmer notes that most evidence points to the homology of the lacrimal bone of birds with that of the nonavian archosaurs: (1) the lacrimal always forms the caudal margin of the antorbital fenestra in all archosaurs, including birds; and (2) in the dinosaurs leading to birds the prefrontal is progressively reduced in size and the lacrimal is enlarged. See Cracraft (1968) for a comprehensive review on variation of the lacrimal bone. See Annot. 107, 111.

(111) Facies articularis frontonasalis. This is the surface of Os lacrimale that articulates with both Os frontale and Os nasale; in some birds the lacrimal bone articulates medially with the ectethmoid and occasionally with Os jugale. See Arthr. Fig. 5.2.

(112) Columna vertebralis. The total number of vertebrae as well as the number of regional vertebrae varies in different avian taxa. The total number ranges from 39-64 (pygostyle counted as one vertebra). Fewest vertebrae occur in passerine birds; most occur in the swans and ratites. Most interspecific variation in numbers occurs in the cervical series of vertebrae (see Annot. 129). Individual variation in number of vertebrae within taxa is common.

(113) Partes vertebrae. See the review papers of Komarek (1970), and Zweers, et al. (1987) for a detailed treatment of the nomenclature of the features of avian vertebrae. Following Boas (1929) the names of the parts ofa vertebra listed herein are based mainly on a hypothetical "typical" cervical vertebra of Boas' Segment II (see Annot. 129); however, the cervical vertebrae lack distinct, prominent transverse processes such as possessed by the thoracic, synsacral, and caudal vertebrae. Dorsally each vertebra consists of an arch (Arcus vertebrae) and a ventral body (Corpus vertebrae). The opening enclosed by the two is the Foramen vertebrale. Collectively the entire series of the vertebral foramina produce the Canalis vertebralis that houses the spinal cord, its meninges, and the internal vertebral venous sinus (yen. Annot. 46). The arch and body bear several processes which are lever arms for muscle attachment or articular surfaces connecting vertebrae (see Annot. 127a; and Arthr. Annot. 60).

Corpus vertebrae. The Corpus of typical cervical and thoracic vertebrae has expanded cranial and caudal ends, with a constricted midsection, the Concavitas lateralis. The Facies dorsalis corporis (the spinal cord surface of the vertebral body) is not flat, but forms a longitudinal sulcus.

Birds are the only vertebrate animals in which most of the intercorporal articular surfaces are heterocoelus or saddle-shaped (Fig. 4.8). Of infrequent occurence (e.g., penguins, auks, gulls) the vertebrae in the thoracic region are opisthocoelous, having concave caudal articular surfaces (Beddard, 1898). Martin (1987) notes that certain modern birds (e.g., charadriiforms) still retain amphicoelous vertebrae in the region "just anterior to the sacrum" (see Arthr. Annot. 60). The vertebrae of Archaeopteryx and Ichthyomis are amphicoelous, although hesperornithiformes are heterocoelous.

(114) Fovea cranioventralis. Synonymy: Fovea anteroventralis (Boas, 1929). This pit (Fig. 4.8) accomodates the ventral lip of the articular surface of the body of the vertebra cranial to it upon ventral flexion of the neck.

(115) Sulcus lateralis. The groove on the side of the body of a cervical vertebra (Facies lateralis) accommodating the ascending vertebral artery and vein. Tuberositas lig. collateralis. Synonymy: Tuberositas lateralis corporis (Landolt and Zweers, 1985). The caudal end of each vertebral body exhibits on its lateral side a distinct marking for attachment of Lig. collaterale. See Arthr. Annot. 60.

(116) Eminentia costolateralis. Synonymy: Proc. costolateralis (Boas, 1929); parapophysis; Tuberculum costarium (Komarek, 1979). The costolateral eminence is a small prominence of the lateral surface of the bodies of thoracic vertebrae that bears an articular facet, Fovea costalis, for the head of a rib, Capitulum costae. The fovea occurs on free thoracic vertebrae as well as those of the notarium and synsacrum. Replacement of Komarek's term "tuberculum costarium" avoids confusion with the tuberculum of a rib (see below, Annot. 117 and Arthr. Annot. 79.

(117) Fovea costalis. Articular surface on the lateral end of a transverse process of a vertebra for the tubercle of the rib, Tuberculum costae. The costal fovea also occurs on the Eminentia costolateralis (see Annot. 116; and Arthr. 79).

(118) Proc. costalis. Synonymy: Spina laminae ventralis (Komarek, 1970); Pleurapophysis. A rudimentary rib with its proximal end ankylosed to the Corpus and Proc.transversus of a cervical vertebra, its free caudal end forming an attenuated style or spine (Fig. 4.8). See Annot. 141b regarding the costal processes of sacral vertebrae.

(119) Crista [Proc.] ventralis corporis. Synonymy: Hypapophysis; Proc. latus (Boas, 1929); Crista ventralis (Komarek, 1979). These median, ventral crests (processes) display interspecific variablity in shape and relative development.  Crest" is descriptively apt for laterally compressed, plate-like processes. The crests are present on the ventral side of the bodies of the cranial and caudal series of cervical vertebrae, but lacking in the intermediate series (see Annot. 129). The size of the ventral crest on the Atlas of different avian taxa is variable; that of the Axis is quite strong in many birds (see Boas, 1929).

Ventral crests are most strongly developed on the cranial series of thoracic vertebrae and the cervicothoracic transitional vertebrae of spheniscids, Gavia, alcids, and some anseriforms (Beddard, 1898). They are considered adaptations for powerful underwater use of the neck (Kuroda, 1954). See below Annot. 122; and Arthr. Annot. 72. The paired ventral longus colli muscles are attached to the crests (Myol. Annot.56).

Fenestrae intercristales. Synonymy: Foramina intercristales (Komarek, 1979). The ventral crests of cranial thoracic vertebrae (including those of the Notarium) of some taxa are ankylosed to one another. The fenestrae are windows (openings) of variable size and shape where the ventral intercristal ligaments are incompletely ossified, in other words, incomplete fusion of adjacent ventral crests (see Annot. 140); Arthr. Annot. 63).

(120) Alae cristae ventralis. Paired wing-like lateral extensions of the ventral edge of the Crista ventralis; seen in the cranial series of thoracic vertebrae of certain diving birds, e.g., Cavia (Kuroda, 1954); slightly developed in Anas (Landolt and Zweers, 1985) and alcids (Strauch, 1985). According to R. W. Storer (pers. comm.) the alae are best developed in the loons, next in some penguins (Aplenodyles), present in all alcids, and fairly well developed in the larger alcid species (Alca, Uria, Pinguinus, Fratercula) and the diving ducks (e.g., Clangula).

(121) Proc. caroticus. Synonymy: Catapophysis (Beddard, 1898); Proc. sublateralis (Boas, 1929); Proc. hemalis (Komarek, I 970a) . Paired incurved processes on the ventral side of vertebral bodies of the intermediate group of cervical vertebrae (Fig. 4.8B; Annot. 129). The carotid processes are not homologous with the haemal processes of the tail region of birds and other vertebrates (Annot. 144).

Each of the carotid processes forms the lateral wall of the Sulcus caroticus. Slips of M. longus colli ventralis (Myol. Annot. 56) are attached to the carotid processes. In most birds the free ends of a pair of carotid processes are connected by a ligamentous bridge producing a short canal. In certain birds, e.g., Pelecanus, Ardea, Dendrocopos. the paired processes become ankylosed, forming a complete osseous canal (see below). Fused processes are thought to be convergent fearures in species having the ability to throw the head forward (Jenni, 1981). In Dendrocopos the fused carotid processes are equipped with a ventral median crest; Jenni (1981) considers that the crests are adaptations for drilling and drumming (see Annot. 119).

Canalis caroticus cervicaIis. Synonymy: subvertebral canal. On the ventral surface of the intermediate segment of the cervical vertebral column the internal carotid arteries course in this osseo-fibrous canal that is partially formed by the carotid processes (Annot. 121a, 99). See Art. Annot. 15.

Proc. postlateralis (Zusi and Storer, 1969). Synonymy: Proc. inferolateralis (Boas, 1929); Proc. ventrolateral is (Landolt and Zweers, 1985). Seen in ventral view of cervical vertebrae, this process in grebes is a paired caudolateral projection of the vertebral body; for attachment of M. longus colli ventrales (Zusi and Storer, 1969). Present also in Morus and Phoenicopterus.

(122) Crista ventrolateraIis. Synonymy: Proc. inferolateralis (Boas, 1929); Proc. ventrolateral is (NAA, 1979). Ventrolaterally oriented, paired projections attached to the ventrolateral border of the body of certain thoracic vertebra; the ventrolateral crests flank the Crista ventralis on each side; present, e.g., in Larus, and the owls, Strix, Nyctea. See Fig. 4.8A.

(123) Proc. transversus vertebrae. Synonymy: Diapophysis. Paired process that projects laterally from each side of the vertebral arch. During postnatal maruration of the skeleton the transverse processes of cervical vertebrae become fused with cervical ribs (see Annot. 134, 138). The transverse process of most of the cervical vertebrae is not a pronounced fearure as in the thoracic, synsacral, and caudal regions (see Annot. 134, 135); it is often indistinguishable from the Ansa costotransversaria of cervical vertebrae in marure birds (Annot. 135).

(124) Crista transverso-obliqua (Boas, 1929). The cervical vertebrae of longnecked birds best exhibit this crest on the dorsal surface of the vertebral arch. The crest of each side extends obliquely caudolateralIy onto its caudal zygapophysis.

(125) Torus dorsalis. Synonymy: Hyperapophysis (Beddard, 1898); Processus dorsalis (Boas, 1929). This boss of bone is found on the Crista transversc-obliqua of the dorsum of the caudal zygapophysis (Fig. 4.80); for attachment of Mm. ascendentes (see Myol. Annot. 46-49). The location of the torus varies from the base to near the tip of the zygapophysis; it is strongly developed on cervical vertebrae of some forms (e.g., Alca, Haliaetus, Morus). The use of "Torus" is preferable since it avoids confusion with the spinous [dorsal] process of the vertebral arch.

(126) Area lig. elastici. Synonymy: Facies lig. e1astici (Komarek, 1970). Interlaminar and interspinous elastic ligaments are usually ·attached cranially and caudally on the dorsal lamina of the vertebral arch at the base of Proc. spinosus [dorsalis]. Bony markings of the ligaments are variously developed as roughened ruberosities, facies, fossae, or foveae that are here designated generically as "areae". See Arthr. Annot. 63.

(127a) Arcus vertebrae. Each end of the vertebral arch is attached to the dorsolateral border of its vertebral body; the arch forms the lateral wall (Lamina lateral is arcus) and the dorsal wall (Lamina dorsalis arcus) of the vertebral canal (see below). The transverse process is a lateral projection of the arch;  ts base marks the dividing line between lateral lamina and dorsal lamina, best exhibited in thoracic vertebrae since cervical vertebrae lack prominent transverse processes. The level of the zygapophyses indicates the dividing line between dorsal and lateral laminae in cervical vertebrae.

Lamina lateralis arcus [Pediculus arcus]. Lamina lateralis is a substitute name for the mammalian "Pediculus". In birds the lateral part of the vertebral arch is plate-like rather than a constricted stalk (pedicle) as in mammals; this lamina is especially . expansive in the "long vertebrae" of birds (Komarek, 1970a). See Annot. 128a.

Lamina dorsalis arcus is the segment of the vertebral arch that extends from the base of the transverse process of one side to that of the opposite side; it bears the Proc. spinosus on the midline of its dorsal aspect. See Annot. 128 b, c.

(127b) Lamina arcocostalis (Landolt and Zweers, 1985). This lamina is a thin shelf of bone continuous with the caudal margin of Ansa costotransversaria (Fig. 4.8D); the lamina extends lateroventrad from the vertebral arch often over the entire length of the spine of the costal process in anserids and anatids. In Gallus and Phoenicopterus the arcocostal lamina is less extensive, not reaching the tip of the costal process. The lamina may be considered as an extension of the Ansa which forms the dorsolateral wall of a craniocaudally-attenuated transverse foramen whereby the foramen becomes converted into a canal (see Annot. l27c).

(127c) Lamina corporocostalis (new term; well illlustrated, but not named by Komarek, 1979: 106). In conjunction with the occurrence of the arcocostal lamina, another lamina, the corporocostal lamina, extends medially from the costal spine to the vertebral body. It forms the ventral floor of the attenuated transverse foramen (canal) in the birds noted in the paragraph above. Both the arca- and corporocostal laminae are derived by ossification of intermuscular aponeuroses or fascial sheaths (see Myol.).

(128a) Incisura caudalis/cranialis arcus. Synonymy: Incisura vertebralis (Komarek, 1979). These are notches in the cranial and caudal borders of the Lamina lateralis arcus. The cranial notch of one vertebra and the caudal notch of the vertebra in front of it together form the boundaries of a Foramen intervertebrale for passage of the spinal nerve and vessels into and out of the vertebral canal. The caudal incisure is generally markedly the deeper of the two (Annot. 143a).

(l28b) Hiatus interarcualis. The opening or gap between the dorsal laminae of the arches of adjacent (articulated) vertebrae as seen in dorsal view (see Zusi, 1962; Komarek, 1979). The hiatus is closed by the interlaminar elastic ligaments and membranes (see Arthr.). The hiatus is bounded by the Lacunae interzygapophysiales of the dorsal laminae of the arches of two adjoining vertebrae (see below), most pronounced in the cervical region (see below).

(128c) Lacuna interzygapophysialis (new term). "lncisura arcualis" (Komarek, 1970), has been replaced to avoid confusion with the lncisurae cranialis/caudalis arcus (of Lamina lateralis) that are boundaries of the intervertebral foramina. The Lacuna is the V-shaped or often broadly V-shaped indentation of the Lamina dorsalis of the vertebral arch, located between the right and left zygapophyses (Fig. 4.8C) at each end of a vertebra (see paragraph above); two adjoining lacunae form the cranial and caudal boundaries of the Hiatus interarcualis.

(129) Vertebrae cervicales. The greatest number of cervical vertebrae are found in ratites (ca. 20) and in swans (23-25); fewest in coraciiforms and passeriforms. Boas (1929) characterized the cervical vertebral column as consisting of three morphologically and functionally distinct sections: Segment I, the most cranial series, Segment II, the intermediate series, and Segment ill, the most caudal series. Zusi (1962) noted that the joints within and between the segments permit I and III to be flexed ventrally, but Segment II can be flexed only dorsally; this arrangement allows the neck to be held in its characteristic S-shaped retracted position. In birds generally, most of the cervical vertebrae are invaded by diverticula of the cervical system of air sacs (see below); however Boas (1929) reported that all of the cervical vertebrae were apneumatic in the following diving birds: Colymbus (Gavia) , Plotus (Anhinga) , Podiceps, Aica, and Spheniscus.

(130) Atlas; Axis. These are the specialized first and second cervical vertebrae, respectively. The Axis is also known as Epistropheus. The Atlas is apneumatic in all birds examined, the Axis being apneumatic in many birds (Boas, 1929).

(131) Fossa condyloidea. Synonymy: ventral semi-ring (Boas, 1929). Cupped-shaped or semicircular concave surface of the Atlas for articulation with the occipital condyle of the base of the skull.

Incisura fossae; Foramen fossae. The condyloid fossa on the cranial aspect of the Atlas may be perforated (Foramen fossae) or have an open dorsal notch (Incisura fossae) in which the apex of the dens rides. See Arthr. Fibrocartilago atlantis.

(132) Zygapophysis caudalis [Proc. articularis caudalis]. Synonymy: postzygapophysis. Zygapophysis cranialis [Proc. articularis cranialis]. Synonymy: prezygapophysis. The zygapophysis is one of four processes of each vertebra that project from the vertebral arch or the base of the transverse process. The pair of cranial zygapophyses of one vertebra and the pair of caudal zygapophyses of the vertebra in front form freely moveable synovial joints on each side. The free caudal vertebrae of most birds lack zygapophyses; exception: the albatross Diomedea (see Annot. 128c; Arthr. Annot. 65).

Caudal zygapophyses are present on the Atlas of most birds studied by Boas (1929), thus paired atlantoaxial zygapophysial articulations exist. See Arthr. Annot. 68.

(133) Proc. costalis atlantis. A rudimentary rib is not evident on the Atlas of most birds (Boas, 1929); therefore the Atlas of relatively few birds exhibits transverse foramina (see Annot. 134, 135). Boas (1929) depicted well developed, complete transverse foramina of the Atlas in Rhea and Cygnus, incomplete ones in other forms. See Annot. 118, 123, 134, 138.

(134a) Foramen transversarium. Synonymy: Foramen costotransversarium. The transverse foramen characterizes most of the cervical vertebrae of birds (for exception, see Annot. 133). Even though the avian transverse foramina may have considerable length and might be referred to as canals (Annot. l27b, c), the term "Foramen transversarium" is retained for consistency with the mammalian nomenclatures. See below, Annot. 135 for the fetal derivation of the foramen.

(134b) Canalis vertebrarterialis (Boas, 1929). On each side of the cervical vertebral column the series of transverse foramina forms this canal that extends the length of the cervical column and conducts the ascending vertebral artery and companion vein(s) (Art. Annot. II).

The cervical transverse foramen is the equivalent of the opening formed in the angle between the tuberculum and capitulum of each rib and the transverse process of a thoracic vertebra (see Fig. 4.8A, B; Annot. 148). Thus the series of thoracic costovertebral openings is morphologically equivalent to the cervical vertebrarterial canal; moreover, it carries the descending vertebral vessels (Art. Annot. 11) as well as loops of the paravertebral autonomic nerve trunk.

(135) Ansa costotransversaria (Boas, 1929). Synonymy: Lamina ventralis (Komarek, 1970). The Ansa (L. loop) is formed by postnatal ankylosis of the rudimentary cervical rib (Costa cervicalis) with the transverse process and vertebral body of a vertebra. Thus the ansa represents part of the external wall of a transverse foramen, and the body (and lateral lamina of the vertebral arch) form the medial wall (Fig. 4.8B) The ansa demonstrates suiface features: a knob-like Tuberculum ansae (Knopffortsatz, Boas, 1929) and a series of linear Cristae laterales (Langskanten,  Boas, 1929). These features mark the attachment of tendons of lateral cervical musculature (Myol. Annot. 53, 54).

(136a) Incisura caudalis arcus. The caudal notch of the arch of the Atlas forms the rostral boundary of the atlanto-axial intervertebral foramen for the second cervical spinal nerve (see Annot. 128a).

(136b) Dens axis. Synonymy: Proc. odontoideus. The joints between the avian Axis and Atlas differ from those of 'mammals: in addition to the articulation of the Dens with the Atlas, an Artc. intercorporea and paired zygapophysial articulations are present. The atlas and axis are ankylosed in adult hornbills (Bucerotidae) (Kemp, 1985).

(137) Proc. spinosus [P. dorsalis] axis. Although commonly present, the spinous process is lacking from the Axis of some forms (e. g., the scolapacid, Gallinago delicata).

(138) Proc. costalis axis. The rudiment of a rib is present on the Axis of many, but not all, birds that have been studied; occasionally weak projecting tips of the costal processes are found (Boas, 1929). When present, Proc. costalis forms an arch and completes the transverse foramen. See Annot. 133, 135.

(139) Vertebrae thoracicae. Synonymy: Vertebrae dorsales. The first thoracic vertebra is defined as the cranialmost vertebra with a complete rib (i.e., having vertebral and sternal segments) that articulates directly or indirectly with the sternum (see Annot. 147). The vertebrae at the root of the neck that bear moveable ribs, notreaching the sternum, have been called "Vertebrae cervicodorsales" (Newton, 1896;Zusi, 1962); these are transitional in configuration between cervical and thoracic vertebrae. See Annot. 141a; and Arthr. Fig. 5.10).

(140a) Notarium. Synonymy: Os dorsale. The Notarium (Ok. noton, back) is a unit of several (2-6) (Barkow, 1856; Storer, 1982) thoracic vertebrae that are coalesced rather completely in adults, but not fused with the synsacrum (see Arthr. for significance of the joint between the notarium and synsacrum). The Notarium (Fig. 4.9) is characteristically present in at least 17 families of birds, occasional in several others: tinamous, Pelecanus. threskiomithids (ibis and spoonbills), galliforms, columbiforms, as well as all podicipediforms and most falconids (Storer, 1982). The Mesozoic birds Archaeopteryx and Gobipteryx possess several "fused anterior dorsal (thoracic) vertebrae" (Martin, 1987).

In certain birds (e.g., larids, rhynchopids, gruids, Branta and Anser) consolidation of the thoracic vertebral column is achieved by ossification or calcification of the epaxial muscle tendons that interdigitate and may fuse to one another and to the transverse and spinous processes of adjacent vertebrae. This sort of consolidation as well as the rather complete synostotic coalescence (above) are both found in some groups (e.g., grebes and cranes; R. W. Storer, pers. comm.). See Arthr. Annot. 71.

(l40b) Canalis notarii. The segment of the vertebral canal that traverses the Notarium (see Annot. 144). Crista spinosa [dorsalis] notarii. Synonymy: Crista dorsalis notarii (NAA, 1979). Crest formed by the ankylosed spinus processes.

(141a) Synsacrum. Synonymy: Os lumbosacrale; Os pelvicum. A rigid unit consisting of ankylosed vertebrae in mature birds (Figs. 4.9, 11). The preacetabular part of the Synsacrum incorporates one or several thoracic vertebrae and the "lumbar series" (synsacral segment II of Boas, 1933) that are attached to the preacetabular ilium: the proper sacral vertebrae are opposite the acetabulum (see below); several more of the proximal caudal vertebrde caudales (urocaudals, Parker. 1888) comprise the postacetabular series. Interspecific variation exists in the number of vertebrae forming the synsacrum. See Barkow (1856), Boas, (1933), and van Oort (1905) for detailed comparative studies of the synsacrum in different taxa.

The synsacrum is synostosed on each side with the Os coxae, the three elements forming the bony pelvis; the pelvis and uropygium (fopog. Annot. 36) together form the dorsal abdominal wall (Baumel, 1988). See Arthr. Artcc. synsacri.

(141b) Vertebrae sacrales. One or two "true" sacral vertebrae (Segment III vertebrae of Boas, 1933) are identified by their conspicuous costal processes, lacking in the vertebrae to the front and rear of them. In some birds the costal processes of the sacral vertebra(e) extend laterally to the hip bone near the acetabulum, thus the name, Vertebra acetetabularis (Du Toit, 1912-13; Komarek, 1979; Radu, 1975) which is well exemplified in the pelvis of Larus, Stm, Gallinula. See Fig. 4.9.

(141c) Lamina transversa notarii/synsacri. During skeletal maturation the transverse processes of the notarial and synsacral vertebrae become coalesced, producing on each side a continuous transverse lamina. In mature birds the lateral border of each Lamina of the synsacrum becomes firmly ankylosed with the hip bone (Os coxae) of its side. In instances where the fusion between the transverse processes is incomplete, the persistent windows are known as Fenestrae intertransversariae. The fenestrae as well as smaller foramina are traversed by nerves and vessels. SeeFigs. 4.9, 11.

(142a) Corpus notarii/synsacri. This is the unit of consolidated vertebral bodies (corpora) that form the median, ventral column of bone of the notarium and that of the synsacrum.

142b) Facies visceralis synsacri. Synonymy: Facies abdominalis. See Barkow (1856) and Boas (1933) for features of this ventral (internal) surface of the synsacrum which is in contact with abdominal organs (viscera).

(142c) Crista spinosa [dorsalis] synsacri. The crest formed by the ankylosed spinous processes of the synsacral vertebrae. .

(143a) Foramina intervertebralia. Dual intervertebral foramina may exist in some birds over part of the length of the synsacrum, especially immature ones; these are separate openings for the dorsal and ventral roots of the spinal nerve, the roots uniting external to the vertebral canal (e.g., Struthio, Rhea, Somateria, Porphyrio, Alca, Corvus) (Boas, 1933).

(143b) Canalis synsacri [vertebralis]. See Annot. 140b. The part of the vertebral canal of the synsacrum. The canal is enlarged along the middle of its length; the enlarged chamber contains the lumbosacral intumescence of the spinal cord which is known as the Cranium inferior (or ischiadicus) by older authors (Barkow, 1856).

(144) Proc. haemalis. Synonymy: intercentrum; chevron bones. Found only on the rear three or so caudal vertebrae on their ventral surfaces, including the pygostyle. Prominent in large birds (e.g., albatross, penguin, heron, pelican) and in some smaller forms (e.g., Crotophaga, Dendrocopos); inconspicuous and vestigial, e.g., in the pigeon and chicken. The haemal processes are usually ankylosed to the cranial ends of the vertebral bodies, projecting ventrocranially and underlying the intervertebral discs and rear of the vertebra ahead. In Crotophaga the processes are fused at their bases with the vertebral body, and also articulate firmly with the body of the vertebra cranial to it.

In some mature birds certain of the haemal processes occur as distinct nodular elements artached by ligaments to the discs and/or to the vertebral bodies (Diomedea sp.). The haemal processes are persistent intercentra (Piiper, 1928), an element of embryonic vertebrae; absent in other vertebral regions except the atlas and axis. Archosaurs closest to birds lack intercentra in the vertebral column except in the tail and CI, C2. See Annot. 121 for comparison with cervical carotid processes.

(145) Pygostylus. Synonymy: Urostylus; Coccyx. Compound bone formed by postnatal ankylosis of 3-6, commonly 5-6, of the terminal free caudal vertebrae. The fetal development of the pygostyle is reviewed by Steiner (1938) and van Oort (1905). Holmgren (1955) contended that the Ostrich pygostyle is not homologous with that of carinate birds, a claim refuted by de Beer (1956). See Baumel (1988) for the structures artached to the pygostyle, its relationships, and remarks on its evolutionary significance.

(146) Basis pygostyli. Derived from fusion of the several vertebral bodies incorporated into the pygostyle. Lamina pygostyli. Blade-like portion of pygostyle derived from vertebral spinous processes and arches. Rudimentary transverse processes are present on the pygostyle of certain piciforms (Burt, 1930: 478). Discus pygostyli: In woodpeckers (piciforms) especially, and other scansorial birds, the 'pygostyle is distinguished by a strong transverse, shield-like disc on its caudal margin (Burt, 1930), the disc serving as an expanded area of attachment for the extraordinarily well developed muscles that depress the tail.

(147) Costae. The freely moveable ribs of different avian taxa vary in number. Ribs of the cervicothoracic transitional region of the vertebral column are short "floating ribs" that fail to reach the sternum (Costae incompletae). The so-called "true ribs" (Costae completae verae) consist of vertebral and sternal elements; the sternal segments articulate with Margo costal is stemi (see Annot. 157). In some instances the sternal part of one or more of the ribs do not articulate directly with the sternum (Costae completae spuriae), but with the sternal parts of true complete ribs cranial to them. Caudal to the true ribs a variable number of floating vertebral ribs may occur; the last of the series of true ribs often articulates with the ventral side of the preacetabular ilium in various birds (Artbr. Annot. 80).

(148) Proc. uncinatus. Synonymy: Appendix epipleuralis (Shufeldt, 1890). Dorsocaudally oriented process attached to the caudal border of the vertebral ribs. Screamers (Anhirnidae) and megapodids lack uncinate processes (R. W. Storer, pers. comm.). See Myol. Annot. 59.

Incisura capitulotubercularis. The neck region (collum) of a vertebral rib exhibits this notch between its capitulum and tubercle. The interval between the neck and the transverse process of the vertebral rib corresponds to the transverse foramen of the cervical vertebrae. See Fig. 4.9; Annot. 134.

Sulcus pulmonalis. The elongated sulcus between the dorsal parts of adjacent ribs. The sulcus is occupied by lung tissue, the Torus intercostalis (Resp. Annot. 49); each Torus is in contact with the ribs cranial and caudal to it, as well as with the intercostal muscles and parietal pleura.

(149) Sternum. See Fürbringer (1888) for a detailed synonymy for the parts of the avian sternum. He distinguished a cranial part, the "Costosternum", to which the ribs are attached. and a caudal part, the "Xiphosternum", also referred to as Metasternum.

Corpus sterni. Synonymy: Tabula sterni.

(150) Proc. craniolateralis sterni. Synonymy: Proc. sternocoracoideus; Proc. precostalis.

Proc. caudolateralis sterni. Synonymy: Proc. posterior lateral is sterni or Proc. xiphoideus lateralis stemi (Fürbringer, 1888). Fiirbringer noted that some galliforms possess this distinctive, extraordinarily elongated, lateral process of the sternum that branches into strong lateral and medial trabeculae. See Annot. 151.

(151) Incisurae et fenestrae sterni. The caudal part of the sternum is notched (incisurae) or perforated (fenestrae) in a variety of ways in different avian taxa (Fig. 4.11). Bars of bone between incisurae/fenestrae are referred to as "trabeculae"; the openings in the sternum are closed by fibrous membranes. See Fiirbringer (1888) for illustrations of the various patterns.

(152) Facies muscularis sterni. Synonymy: Facies ventralis or externa. The surface of Corpus stemi lateral to the base of the carina to which the pectoralis and supracoracoid muscles are attached.

Facies visceralis sterni. Synonymy: Facies dorsalis or interna. Inner surface of sternum related to heart and liver.

(153) Linea intermuscularis. M. supracoracoideus is attached to the ventral surface of the Corpus sterni and to the adjacent lateral aspect of the Carina sterni (Myol. Annot. 76). The intermuscular lines on each surface mark the bony attachment of the dense fascia that invests the muscle and separates it from M. pectoralis.

(154) Planum postcarinale. Synonym: Planum postpectorale (Fürbringer, 1902). The Carina stemi does not reach the caudal margin of the sternum in some forms (e.g., pelecaniforms). The planum is therefore the continuous bilateral flat surface of Facies muscularis of the sternum caudal to the carina.

(155) Pila costalis. The column of bone that reinforces the costal margin of the sternum, prolonged onto the Trabecula lateralis in some birds (Fig. 4.11).

(156) Sulcus articularis coracoideus. Synonymy: coracoid groove or depression. Located at the cranial margin of the Corpus stemi, this is the surface for articulation with the coracoid. The sulcus is a narrow, attenuated, curved groove on each side of the sternum; it extends from the base of the craniolateral process medially to the side of Rostrum stemi or onto its dorsal surface (e.g., Larus, Branta). In some birds the Sulcus is directed caudolaterally from the midline Rostrum; however in others it is oriented nearly transversely (e.g., Gallus, Coccyzus, Dendrocopos, Progne). In several groups the coracoidal sulci overlap in the median plane (see Arthr. Annot. 89, 90). Commonly the length of the Sulcus is nearly perpendicular to the median plane, but its lateral end is depressed or elevated in some birds. See Fig. 4.11.

(157) The Margo costalis sterni, when viewed from the side, exhibits a series of notches (Incisurae costales) separated from one another by partitions, each known as a Proc. articularis sternocostalis (Komlirek, 1979). Between two adjacent processes is a small compartment called the Loculus costalis (new term); the head of the sternal rib partly occupies a locule, and articulates with the caudal surface of a sternocostal articular process, Facies articularis costalis. In some avian taxa dual articular facets exist for the corresponding facets on the dual-headed sternal ribs (see Arthr. Annot. 83).

Margo caudalis sterni. The caudal margin of the sternum is highly variable in shape; it may be squared, rounded, intact, or notched. See Fürbringer (1888) for characteristic shapes of sterna of numerous taxa.

(158) Pila coracoidea. The transversely oriented, curved pillar of bone along the cranial margin of the Corpus sterni (Fig. 4.11) that strengthens the articular sulcus for Os coracoideum.

(159) Rostrum sterni. Synonymy: Manubrium sterni; Spina intercoracoidea sterni (see Fiirbringer, 1888, for complete synonymy and descriptions and summary of variation of the Rostrum). Serves as an attachment of pans of Membrana sternocoracoclavicularis (Arthr. Annol. 86). The spines of the Rostrum are designated Spina externa and Spina interna because of their continuity with the external and internal labra of the Sulcus articularis coracoideus. Spina externa is usually present; in some psittacines, picids, and most passerines, including the Menurae, the external spine is forked, its processes are called the Alae spinae externae. The Spina interna is of much less frequent occurrence (occurring in, e.g., galliforms, cuculids, meropids, upupids, and bucerotids), and is frequently represented by a tubercle(s) between the two Labra interna of the coracoidal articular sulcus. The external and internal spines may coalesce producing the Spina communis (see Fig. 4.11; Annot. 160).

(160) Foramen rostri. Synonymy: Foramen interspinale. The foramen is an opening at the base of the ankylosed external and internal spines of the sternal rostrum (e.g., galliform and coraciiform birds). In some birds the Septum·interarticulare connects the external and internal spines, and separates the right and left coracoidal sulci in the midline by bone or membrane; in birds having side-to-side or overlapping contact between the two coracoids the Spatium intercoracoidale is open (Arthr. Annol. 90).

(161) Carina sterni. Synonymy: Crista sterni (Fiirbringer, 1888); (Carina, L. keel). The vertical plate of bone attached to the median line of the Corpus sterni found in most birds (thus "carinate birds"). In the psittaciform, Strigops, the carina is lacking. Ratites generally lack a distinct, well developed carina, e.g., Struthio. The sternum of Apteryx, Casuarius, and Rhea exhibits a slight crest (Beddard, 1898).

Crista lateralis carinae. A paired crest on each side of the dorsal, thick pan of the cranial margin of the carina (e.g., Gallus, Cathartes). The Sulcus carinae is the shallow groove between the two lateral crests; the Sulcus is an elongated triangle in Gallus. The Pila carinae (Fig. 4.11) is the thick reinforcing pillar of bone of the cranial margin of the carina.

(162) Clavicula [Furcula]. (Fig. 4.10. (Furcula, L. fork). Furcula refers to the united, paired clavicles. When not ankylosed at their ventral ends, the clavicles may be joined by cartilage or fibrous tissue (many parrots, owls, Buceros, Alcedo; Newton, 1896). Olenny and Friedmann (1954) discussed the reduction or suppression of the clavicle in various birds (e. g., Australian parrots). According to Austin (1961) the scrub bird Atrichornis is the only passerine with noncoalesced clavicles (see Rich, et al., 1985). The clavicles are absent in all ratites except for the emu (Elzanowski, 1989).

Fürbringer (1888) describes subcoracoid, acrocoracoid, and supracoracoid segments of the clavicle, the last extending to the scapula, and presented a summary of the form of the clavicle. See Stegmann (1964) for the functional implications of the configuration of the clavicle. Jenkins, et al. (1988) have observed cineradiographically movements of the clavicle during flight. See Arthr. Annot. 85.

(163) Apophysis furculae [Hypocleideum]. Synonymy: Lamina interclavicularis. In most birds the ventral pan of the Furcula is drawn out into a median projecting blade, rod, or knob that is attached to the Apex carinae directly or indirectly (see  Arthr. Annot. 85). Fürbringer (1888) describes three varieties of the Proc. interclavicularis, one of which projects proximally into the angle formed by the junction of the two furcular rami.

(164) Extremitas omalis claviculae [Epicleidium]. Synonymy: Extremitas scapularis. Omos, Ok. shoulder). This is the dorsal expanded end of each clavicle at the shoulder (see below, Annot. 165; and Topog. Annot. 32).

(165) Proc. acromialis claviculae; Proc. acrocoracoideus claviculae. Clavicles of certain birds possess distinct processes for articulation with the cranial tip of the scapula (Proc. acromialis) arid the upper, pointed end of the coracoid bone (Proc. acrocoracoideus). In diomedeids, ciconiiforms, and falconiforms only the caudally directed Proc. acromialis of the clavicle is well developed. Both processes are present, e.g., in Alcedo, Merops, Ramphastos, and Sturnus (Fürbringer, 1888).

(166) Scapula. See Fürbringer (1888) for additional terms and comparative descriptions of the avian scapula not listed here. His illustrations depict the range of shapes of avian scapulae. Facies lateralis. Synonymy: Facies externa or dorsolateralis of the scapula. Facies medialis [costalis]. Synonymy: Facies interna or ventromedial is of the scapla.

Acromion. (Omion, Ok. small shoulder). The pointed cranial end of the scapula, near its glenoid process. In Menura and Atrichomis (passerine suborder Menurae) the acromion is bifurcate, having two blunt knob-like processes (Rich, et al., 1985).

Crista Lig. acrocoracoacromiali. In some birds this short crest on the dorsum of the acromion is continuous with the dorsal margin of the scapula; for attachment of the acrocoracoacromiale ligament (Fig. 4.10; Arthr. Annot. 95). The crest is pronounced, e.g., in Cathartes, Ardea, Branta, Phoenicopterus, and Columba.

(167a) Facies articularis humeralis. Synonymy: Pars scapulae fossae glenoidalis; Pars coracoidea fossae glenoidalis (Fiirbringer, 1888). The humeral articular facet of the glenoid process of the scapula adjoins the humeral articular facet of the glenoid process of the coracoid, the two surfaces together forming the Cavitas glenoidalis for articulation with the head of the humerus. The coracoid generally contributes much the larger area to the humeral articular surface (e.g., Strix varia). The slightly concave articular facets of both bones are invested with the thick elastic cartilage (J. Baumel and R. Brown, pers. obs.), Lig. coracoscapulare interosseum, with which the humerus actually articulates; the elevated margins (labra) of this ligament deepen the shallow glenoid cavity (Arthr. Annot. 93).

(167b) Proc. glenoidalis scapulae. Set off somewhat perpendicular to the body of the scapula, the glenoid process of the scapula bears the surface for articulation with the head of the humerus; the glenoid process in certain birds also articulates directly with the procoracoid process of the coracoid. See Fig. 4.10.

Proc. glenoidalis coracoidei. This is the low, lateral offset of the shaft of the coracoid bone that bears the humeral articular surface, usually continuous with the base of the procoracoid process.

(168) Facies articularis coracoidea. Linear articular surface on the cranial extremity of the scapula extending between the acromion and the glenoid process; forms a joint with the procoracoid and adjacent glenoid process of the coracoid bone.

Tuberculum coracoideum. Some birds (e.g., Ardea, Larus, Branta) possess this convex spherical or ellipsoidal boss of the cranial surface of the Proc. glenoidalis of the scapula; the Tuberculum fits into a cupped surface on the coracoid together forming the coracoscapular joint (see Fig. 4.10; and below, Annot. 173b). The coracoscapular joint surfaces in most birds are less elaborate than those just described (see above paragraph).

(169) Tuberculum m. scapulotricipitis. In some birds this distinct tubercle for attachment of the scapulotriceps muscle is located on the ventral border of the scapula directly caudal to its Proc. glenoidalis (Fig. 4.10).

(170) Corpus scapulae. The neck (Collum scapulae) and cranial half of the body (Corpus) of the scapula is generally a rounded cylinder in cross section; its caudal half is flattened and usually blade-like, straight, or curved. The caudal half of the atypical scapula of penguins (spheniscids) is a wide paddle-shape.

(171a) Extremitas omalis coracoidei. The shoulder or dorsal end of the coracoid bone (Omos, Gk. shoulder).

Proc. acrocoracoideus. (Acro-, Gk. combining form, an extremity or highest point of a structure). This is the dorsal end of the coracoid bone that projects past its glenoid process.

(171b) Tuberculum brachiale. Synonymy: Tuber brachialis (Ballmann, 1969a); Tuberositas brachial is (Lambrecht, 1933; Howard, 1929); Tuberositas humeralis. This term refers to the low projection on the medial side of the acrocoracoid process, of the coracoid of some forms which is directed ventrally, overhanging the supracoracoid sulcus to some degree. In the birds in which it exists, the tuberculum is the attachment of the acrocoraco-acromial ligament which forms part of the medial wall of the triosseal canal (Annot. 177) in some birds. Although "Tuberculum brachialis" (sic) is used frequently in avian paleontology, it is not descriptively apt, as the tubercle has no direct relationship to the brachium or humerus.

(172) Proc. procoracoideus (Sabatier, 1880). Synonymy: see Fiirbringer (1888: 41). This is a projection of the medial border of the coracoid, its upper edge roughly perpendicular to the coracoid shaft, its medial border gradually merging with the shaft ventrally. In some birds its tip is curved abruptly dorsally forming the medial boundary of the smoothly curved Sulcus supracoracoideus. See Arthr. Annot. 87, 97.

Sulcus supracoracoideus (Ballmann, 1969a). Groove for the tendon of M. supracoracoideus on the base of Proc. procoracoideus and adjacent part of the upper shaft of the coracoid bone that forms a pulley for the tendon of M. supracoracoideus (Fig. 4.10).

(173a) Facies articularis scapularis. In some birds this narrow, linear facet is on the internal surface of the upper edge of the procoracoid process, and is prolonged laterally onto the base of Proc. glenoidalis (Annot. 168); the continuous surface makes contact with a corresponding surface on the scapula, producing a simple coracoscapular joint (Arthr. Annot. 93). Other birds possess a more complicated joint (see Annot. 173b).

(173b) Cotyla scapularis. Synonymy: Facies scapularis (Ballmann, 1969a). Occurring in some birds (e.g., Ardea, Larus, Branta) , this is the spherical or ellipsoidal concavity on the glenoid process/procoracoid process of Os coracoideum adjacent to its glenoid facet (Fig. 4.10). The cotyla receives the corresponding Tuberculum coracoideum of the scapula, the two forming the coracoscapular joint (Arthr. Annot. 93). In most birds the joint surfaces of the coracoscapular joint are less elaborate than those described here (see Annot. 168 and 173a). The Cretaceous birds Ambionus and Aparomis exhibit the Cotyla/Tuberculum type of coracoscapular joint that Martin (1987) considers primitive for modem birds.

(174) Linea intermuscularis ventraIis (Lambrecht, 1933). Synonymy: anterior intermuscular line (Fisher, 1945). These intermuscular lines on the coracoid are illustrated by Ballmann (1969a). See Myol. Annot. 74, 76.

(175a) Crista articularis sternalis. This surface of the coracoid for articulation with the sternum is divided into ventral and dorsal facets (Facies externa and F. interna). In some birds (e.g., Ardea, Columba, Corvus) they are not continuous with one another. The margins of each of the facets are sharply defined where they meet the superficial and deep surfaces of the coracoid. The external and internal articular facets are set off from one another by a slightly curved ridge (Crista intermedia) that articulates with a corresponding groove at the bottom of the coracoidal articular sulcus of the sternum. In some birds the sternal articular facets of the coracoid are subdivided into medial and lateral parts by a non-articular segment. See Arthr. Annot. 89, 90.

(175b) Facies articularis intercoracoidea. Articular facet located on the medial angle of the sternal end of the coracoid in birds whose coracoids articulate with one another in the median plane. See Annot. 160; Artm.· Annot. 90.

(176) Proc. lateraIis. Synonymy: Proc. lateralis posterior; Proc. externus; Proc. sternocoracoideus. In many birds this process of the sternal end of the coracoid is drawn out into a point, the Angulus lateralis. The upper border of the lateral process is known as the Margo supra-angularis (E. N. Kurochkin, pers. comm.).

(177) Canalis triosseus. Synonymy: Foramen triosseum; Canalis supracoracoideus (Fürbringer, 1888). The canal transmits, and serves as a pulley for, the tendon of M. supracoracoideus. In some birds the canal is produced by only two bones, the procoracoid process of the coracoid and the scapula, with no contribution from the clavicle; the canal may be formed completely by the coracoid alone in birds having an ossified bridge connecting the acrocoracoid and procoracoid processes (e.g., Musophagidae, Meropidae, Upupidae, Bucerotidae, Columba livia, and trochilids). See Arthr. Annot. 87, 95, 171.

(178) Ossa alae [Ossa membri thoracici]. Bones of the wing or thoracic limb. Terms of direction of the wing bones are based on the defined anatomical position of the avian wing, i.e., extended and abducted (see Gen. Intro.). In this anatomical position the extensor (dorsal) aspect of the humerus faces caudally and the flexor (ventral or palmar) aspect faces cranially. The long axis of the ellipsoidal articular surface of the Caput humeri is nearly vertical with the wing outstretched  (Fiirbringer, 1888); the epicondyles at the distal end of the humerus are situated dorsally and ventrally. Of special interest to paleontologists is the work of Ballmann (1969a) which contains a comprehensive terminology for all the skeletal elements of the wing, including attachments of ligaments and muscles. See also Komarek (1979).

Humerus. Consult Fürbringer (1888) for a synonomy of terms on parts of the humerus. Facies caudalis of the humerus is also known as its anconal surface; Facies cranialis is also known as its volar or palmar surface.

(179) Caput humeri. Synonymy: Caput articulare humeri (Fiirbringer, 1888). The head of the proximal end of the humerus, specifically its articular surface.

(180) Incisura capitis humeri. Synonymy: capital groove (Howard, 1929); Incisura collaris. The pronounced notch of the head of the humerus, located between the articular surface of the Caput humeri and Thberculum ventrale (Fig. 4.12A). With the wing folded against the trunk, the incisure accommodates the scapular labrum of Cavitas glenoidalis.

Crista incisurae capitis. The crest or ridge of bone that connects the head of the humerus with the ventral tubercle; the crest separates the proximal end of the incisure of the head of the humerus from the Sulcus transversus (see Annot. 185).

(181) Planum intertuberculare (Fürbringer, 1888). Synonymy: Planum [Facies] bicipitale. The intertubercular plane refers to much of the cranial surface of the expanded proximal end of the humerus distal to its Caput, i. e., the area between the dorsal and ventral tubercles and part of the surface between the bicipital and deltopectoral crests. Features included in this plane are: Sulcus transversus, Impressio coracobrachialis, and Intumescentia humeri. The Planum in most birds is covered by the tendon and aponeurosis of origin of M. biceps brachii.

Sulcus [Canalis] n. coracobrachialis. In many different birds this is a shallow transverse groove at the distal margin of the intertubercular plane of the humerus (see above) which conducts N. coracobrachialis from the distal end of the bicipital crest to the ventral border of the lmpressio coracobrachialis (Fig. 4.12).

Characteristic of charadriiforms (Ballmann; 1979), the nerve is transsmitted by an osseous canal deep to the distal part of the surface of the lntumescentia humeri.

(182) Tuberculum dorsale. Synonymy: Tuberculum minus or laterale; Tuberculum m. supracoracoidei. Located at the proximal end of the deltopectoral crest, for insertion of the principal part of the tendon of M. supracoracoideus. See Fig. 4.12; Annot. 183.

(183) Crista m. supracoracoidei (Fiirbringer, 1888). This crest is an accessory insertion of the tendon of the supracoracoideus muscle, its main insertion being the Tuberculum dorsale. The crest extends distally from the Tuberculum to the base of Crista deltopectoralis. Well displayed in examples of phasianids, alcids, psittacids, and columbids. See Annot. 182.

(184) Crista deltopectoralis. Synonymy: Crista deltoidea; Crista pectoralis; Crista tuberculi minoris, or lateralis, or dorsalis. "Crista deltopectoralis" is used in the paleontological literature (e.g., Ostrom, 1979), and is a reasonable name inasmuch as both M. pectoralis and the cranial head of M. deltoideus major are attached to opposite surfaces of the crest.

Crista bicipitalis. Synonymy: Crista tuberculi majoris, or medialis, or ventralis. Origin of the aponeurosis of the humeral head of M. biceps brachii.

(185) Sulcus transversus (Lambrecht, 1933). Synonymy: Ligamental furrow (Howard, 1929). Located on the cranial surface of the humerus just distal to Caput humeri (Fig. 4.12); for attachment of the Lig. acrocoracohumerale. The sulcus is strongly defined in, e.g., Larus.

(186) Impressio coracohrachialis. An impression for insertion of M. coracobrachialis crdIlialis. The impression is a fairly distinct shallow excavation in many birds, e.g., Branta, Chordeiles, Aegolius, Crotophaga; a deeply etched triangular fossa in larids and charadriids (Fiirbringer, 1888).

(187) Tuberculum ventrale. Synonymy: Tuberculum mediale or majus (Fiirbringer, 1888). The ventral tubercle of the humerus is continuous with the proximal end of Crista bicipitalis (Fig. 4,12), and is much stronger than Tuberculum dorsale. The ventral tubercle is extraordinarily prominent in ratite birds (Fürbringer,  1888); it is a common point of insertion of several of the short muscles of the shoulder region arising from the scapula and coracoid.

(188) Fossa pneumotricipitalis [Fossa tricipitalis]. Synonymy: Fossa pneumoanconaea (Fürbringer, 1888); Fossa pneumatica. This excavation in the proximal humerus varies in its form and development in different avian groups. Its name indicates that parts of the triceps muscle complex and the pneumatic foramen of the humerus are housed in the fossa. The name M. triceps brachii has replaced the term M. anconaeus, requiring a change in Fiirbringer's name of the fossa. The humerus is hardly, or not at all, pneumatic in some avian groups (Fiirbringer, 1888) (e.g., Gavia, Pygoscelis, Alca); in the forms having apneumatic humeri the fossa is present nonetheless, thus "Fossa tricipitalis" is appropriate as suggested by Fiirbringer's term, Fossa anconaea.

Well developed pneumotricipital fossae extend into the Caput humeri and Tuberculum ventrale (e.g., Larus). In most birds the fossa is a single continuous excavation, bounded ventrally and dorsally by Crus ventrale fossae and Crus dorsale fossae (Fig. 4.12) which converge on the apex of the ventral tubercle. The single fossa is occupied by both heads of M. humerotriceps, the insertion of M. scapulohumeralis cranialis and the pneumatic foramen. See Myol. 71-74, 82).

In other birds (also well exemplified by Larus) a second or additional fossa is formed between the Crus dorsalis fossae (medial bar of Bock (1962); Crista coracoidea of Komarek (1979) and the Caput humeri. This second fossa is bounded dorsally by the Margo caudalis of the humerus (Fig. 4.12) that extends from the Caput distally onto the caudal aspect of the shaft of the humerus; the Margo caudalis is a pronounced ridge in many birds, lacking in others. The second fossa is occupied by the dorsal head of M. humerotriceps. Consult Bock (1962) for a comprehensive treatment of this topic in passerine birds; see below, Annot. 189.

(189) Foramen pneumaticum. When present, this foramen (or mUltiple foramina) is located in the Fossa pneumotricipitalis of the humerus (Annot. 188). The pneumatic foramen is not found in the humeri of all birds; humeri of birds with dual fossae generally are not pneumatised. The pneumatic foramen is lacking in: penguins, procellariiformes (except albatrosses), loons, grebes, cormorants and anhingas, several tribes of ducks (mainly the diving ones); most charadriiforms, rallids, and many oscine passerines (S. Olson, P. Ballmann, pers. comms.).

(190) Intumescentia humeri. Term used by Fiirbringer (1888) and Buri (1900) for the convex, smooth swelling distal to, and continuous with, the intertubercular plane (Annot. 181) of the cranial aspect of the proximal end of the humerus; the intumescence is directly opposite Fossa pneumotricipitalis on the caudal side (see Fig. 4.12).

(191) Sulcus n. radialis. A distinct sulcus on the dorsal surface of the shaft of the humerus for N. radialis occurs only rarely: Casuarius, hummingbirds and swifts (Apodiformes).

(192) Condylus dorsalis humeri. Synonymy: Condylus [Trochlea] radialis, or medialis, or internus. With the limb in the anatomical position this condyle on the dorsal (radial) side of the distal end of the humerus articulates with both Radius and Ulna.

Condylus ventralis humeri. Synonymy: Condylus [Trochlea] ulnaris, medialis, or internus; this condyle articulates only with the ulna (see Artbr. Fig. 5.4).

(193) Incisura intercondylaris. Synonymy: Vallis intertrochlearis (Fiirbringer, 1888); Vallis intercondylica (Ballmann, 1969a). Notch separating the dorsal and ventral condyles of the humerus.

(194) Epicondylus dorsalis. [Ectepicondylus]; Epicondylus radialis, or lateralis, or extemus. Epicondylus ventralis. [Entepicondylaris]; Epicondylaris ulnaris, or medialis, or intemus (see Fig. 4.12; Annot. 178; Myol. Annot. 91, 92).

(195) Prot. flexorius. Process at distal end of humerus, ventral to Condylus ventralis of the distal humerus for attachment of the tendinous head of M. flexor carpi ulnaris (Ballmann, 1969a). See Fig. 4.12; Arthr. Annot. 110 (Trochlea humeroulnaris).

(196) Tuberculum supracondylare dorsale. Synonymy: Eminentia m. extensoris metacarpi radialis (E. N. Kurochkin, pers. comm). Most birds possess a relatively compact tubercle on the dorsal border of the distal humerus, a short distance from the dorsal epicondyle (Fig. 4.12) for the origin of M. extensor carpi [metacarpi] radialis (see Myol. Annot. 87). In some birds the Tuberculum is displaced distally, thus so close to the dorsal epicondyle that the two are nearly indistinguishable. In some birds (e.g., diomedids, charadriiforms, passeriforms) the muscle is attached to a stout, pointed Proc. supracondylaris dorsalis. Swifts and hummingbirds are unusual in having the tubercle for M. extensor carpi [metacarpi] radialis displaced far proximally on the humeral shaft (Zusi and Bentz, 1982). See Arthr. Annot. 141; Myol. Annot. 77,78.

Tuberculum supracondylare ventrale. Attachment of Lig. collaterale ventrale of the elbow joint (Arthr. Annot. 105).

(197) Prot. cotylaris dorsalis. Prominent dorsal extension of the proximal Ulna that bears the Cotyla dorsalis on its cranial surface and Impressio m. scapulotriceps on its dorsal surface.

(198) Cotyla dorsalis; Cotyla ventralis. Synonymy: Cotyla externa/interna (Lambrecht, 1933); Facies glenoidalis extema et intema (Ballmann, 1969a). The concave articular surfaces of the ulna for the dorsal and ventral condyles of the humerus. The ventral cotyla is the larger of the two, and is located at the base of the Olecranon (see above and Fig. 4.13).

(199) Incisura radialis. Synonymy: Depressio radialis proximalis (Howard, 1929; BaIlmann, 1969a). The concave facet on the proximal ulna for articulation with Caput radii; situated just past the distal margin of Cotyla dorsalis (Fig. 4.12).

(200) Sulcus scapulotricipitalis. Synonymy: Sulcus m. scapulotricipitis; Sulcus dorsalis m. tricipitis. Sulcus humerotricipitalis. Synonymy: Sulcus m. humerotricipitis; Sulcus ventralis m. tricipitis. Located on the dorsal aspect of the distal humerus, the sulci for the two tendons of the triceps brachii complex are separated by a low ridge; the Sulcus humerotricipitalis is the larger of the two.

(201) Olecranon. Synonymy: Proc. coronoideus ulnaris (Lambrecht, 1933). Strong, pointed process of the proximal end of the ulna for attachment of M. humerotriceps and Trochlea humeroulnaris (Arthr. Annot. 110). Barnett and Lewis (1958) note that the olecranon is lacking in some birds, e.g., the swift Micropus, the penguin Aptenodyres; however this process appears to be replaced by sesamoid bones in the tendons of the triceps muscles in these forms. See Annot. 202.

(202) Os sesamoideum m. scapulotricipitis. Synonymy: Patella ulnaris (Fiirbringer, 1888). This is a sesamoid bone in the tendon of M. scapulotriceps of some species; unusually well developed in the hummingbirds (Zusi and Bentz, 1984) and in spheniscids.

(203) Tuberculum lig. collateralis ventralis (Fig. 9). Synonymy: Facies lig. interni (Ballmann, 1969a). Point of attachment to the ulna of the ventral collateral ligament of the elbow joint (see Fig. 4.13).

Sulcus tendinosus. In some birds this sulcus is a well delineated feature on the ventral surface of the proximal Ulna, located between the Olecranon and the edge of the ventral cotyla; the tendon of M. flexor carpi ulnaris glides in this sulcus, separated from the sulcus by part of Trochlea humeroulnaris (see Arthr. Fig. 5.4).

(204) Facies corporis ulnae. Of the three surfaces of the body of the ulna, Facies caudodorsalis is subcutaneous; the caudodorsal surface is separated from Facies caudoventralis by the row of Papillae remigiales caudales (Annot. 205). Facies cranialis is shallowly concave; its proximal half exhibits pronounced intermuscular crests in some of the larger birds. The flattened ulna (and radius) in spheniscids possesses only dorsal and ventral surfaces.

(205) Papillae remigales caudales; Papillae remigales ventrales. Synonymy: Papillae ulnares anconales (Lambrecht, 1933); quill knobs (Edington and Miller, 1941). Markings on the ulna for attachment of the ligaments of the follicles of the secondary flight feathers. See Fig. 4.13; and Arthr. Annot. 199,204.

(206) Condylus dorsalis ulnae. Synonymy: Condylus extemus or caudalis. CondyIus ventralis ulnae. Synonymy: Condylus intemus, or cranialis, or metacarpalis. As a result of the torsion of the ulnar shaft, the dorsal condyle is located somewhat more caudally than the ventral ·condyle. At the distal end of the ulna the two condyles and the groove between them form the Trochlea carpalis. On the ventral surface of the distal ulna the trochlea is markedly deepened in some birds (e.g., Phoenicopterus) fonning the Sulcus intercondylaris (Fig. 4.13) between the two condyles. Os carpi radiale and Meniscus intercarpalis articulate with both condyles; Os carpi ulnare articulates mainly with the dorsal condyle. See Arthr. Annot. 117-119.

(207) Tuberculum carpale. Synonymy: Tuberositas carpalis (Lambrecht, 1933). The carpal tubercle is a conspicuous, in some birds pointed, process (e.g., Larus) on the ventral aspect of the distal end of the ulna, closely related to the ventral condyle of its trochlea, for the attachment of the Lig. ulno-ulnocarpale distale and Lig. ulnometacarpale ventrale (see Fig. 4.13).

Incisura tuberculi carpalis (new term). This notch between the ventral condyle of the ulna and the Tuberculum carpale is pronounced in some forms (e.g. the vultures Cathanrtes and Coragyps); in these forms the notch contains pneumatic pores. The deep part of Lig. ulno-ulnocarpale distale occupies much of the incisura (Columba).

(208) Depressio radialis. Synonymy: Depressio radialis distalis (Lambrecht, 1933; Ballmann, 1969a); Sulcus radialis (NAA, 1979). This surface of the distal end of the ulna is involved in the distal radioulnar joint, the counterpart of the proximal radioulnar joint. Located on the dorsal surface of the ulna near the carpal tubercle, this surface is the ulnar attachment of Lig. interosseum radioulnare which prevents direct contact of the two bones; the radius glides against the ligament in flexion and extension of the wrist joints. See Fig. 4.12; Arthr. Annot. 116.

(209) Incisura tendinosa (Lambrecht, 1933; Ballmann, 1969a). Situated on the distal end of the ulna near its dorsal condyle, the curved Incisura acts as a pulley for the tendons of Mm. extensor metacarpi ulnaris and extensor digitorum communis as they change direction and enter the manus. The tendons are held in the incisure by a fibrous retinaculum (ossified in Gavia). See Fig. 4.13.

(210) Tuberculum bicipitale radii (Howard, 1929). Synonymy: Tuberculum externum (Lambrecht, 1933). Tubercle on the proximal radius for insertion of M. biceps brachii. In most birds the tendon of M. biceps brachii bifurcates, the main branch inserting on the proximal end of the radius, the other to the proximal ulna.

Tuberculum bicipitale ulnae (Berger, 1966). In the higher passeriforms the radial tendon of the biceps inserts into a fovea (pit), considered by Ballmann (I969a) to be a diagnostic feature. See Fig. 4.13.

(211) Facies articularis radiocarpalis. Synonymy: Articulatio scapholunaris (Lambrecht, 19.33). Surface on the distal radius for articulation with Os carpi radiale. Facies articularis ulnaris. The distal ends of radius and ulna do not directly articulate; the two are closely related but separated by Lig. radioulnare interosseum (see Annot. 208; and Arthr. Annot. 116).

Sulcus tendinosus. A single wide groove, or two parallel grooves (e.g., gaviiforms, McKitnck, 1991), on the dorsum of the distal end of the radius occupied by tendons of extensor muscles of the wrist joint passing across the carpus into the hand.

(212) Depressio ligamentosa. Synonymy: ulnar depression (Howard, 1929). Located on the caudal surface of the distal radius this depression is occupied by the Lig. interosseum radioulnare distale (see Annot. 208; and Arthr. Annot. 116).

(213) Tuberculum aponeurosis ventralis. Synonymy: Ligamental process (Howard, 1929). The Tuberculum is located on the distal end of the radius ventral to the articular surface for Os carpi radiale. The tubercle serves as the attachment of the Aponeurosis ventralis that fans out onto the remiges in the wrist region (Arthr. Annot. 113 and Fig. 4.13).

(214) Ossa carpi. Recently Hinchliffe (1985) has restudied the embryological development of the carpal bones and metacarpals in Gallus, using more precise techniques than those of earlier works. He contends that of the five embryonic carpal elements, the "radiale" becomes the definitive Os carpi radiale. The embryonic "ulnare" regresses and disappears; it is replaced by carpal 'x'. The "pisiform", however, becomes Os carpi ulnare, the definitive adult proximal carpal bone; the latter name is retained because of familiarity. In. early postnatal life the three remaining carpals become incorporated with the proximal end of the metacarpals, forming the compound bone, the Carpometacarpus. For details of the development of the avian wrist and hand and homologies of the digits see Steiner. (1922), Montagna (1945), Holmgren (1955), Romanoff (1960), Berger (1966), Selchert and Richter (1972), and Hinchliffe (1985). See Osteo. Intro. "Nomenclature of digits of wing"; and Arthr. Annot. 112, 122, 128.

(215) Os carpi ulnare (Arthr. Annot. 112, 122). Synonymy: Os cuneiform (Lambrecht, 1933); ulnare. U-shaped carpal bone in the caudal angle of the wrist region; unusual triangular-shaped in spheniscids. Crus longum et Crus breve. These are the two limbs of Os carpi ulnare; Crus longum is situated ventrally, Crus breve dorsally. Proc. muscularis. At the proximal end of the Os carpi ulnare the muscular process projects from the body of the ulnare that connects its two crura; M. flexor carpi ulnaris, Retinaculum ulnocarporemigiale and Lig. humerocarpale attach to the muscular process. See Myol. Annot. 85. .

Incisura metacarpalis is the U-shaped notch between the two crura of os carpi ulnare which clasp the proximal end of the Carpometacarpus. Facies articularis metacarpalis is the surface of the Os carpi ulnare that articulates With the caudal part of the Trochlea carpalis of the Carpometacarpus. .

Os carpi radiale. Synonymy: Os scapholunare (Lambrecht, 1933). On the cranial aspect of the wrist, the radial carpal bone articulates With the distal end of the radius, carpal trochlea of the distal ulna, and the Trochlea carpalis of the Carpometacarpus (see Arthr. Annot. 112, 122).

(216) Os metacarpale alulare. Synonymy: Metacarpus pollicis; Proc. metacarpalis pollicis [digiti I or II]. See Osteo. Intro. for remarks on the nomenclature of digits of the manus.

Extremitas proximalis carpometacarpi. The proximal end of this compound bone is formed by ankylosis of some of the distal carpal bones With the fused proximal ends of the three metacarpal bones (see Annot. 214).

Os prominens. Sesamoid bone in the propatagial ligament' (see Arth. Annot. 141) near its attachment to the extensor process of the carpometacarpus; It is not a carpal bone but is listed with the carpals because of its topographic proximity to them.

Os prominens occurs, e.g., in buteos, falconids, and strigids.

(217) Fovea carpalis caudalis. Synonymy: Fossa carpalis posterior; Fovea carpalis cranialis. Fossa carpalis anterior (Ballmann, 1969a). The foveae are located at the cranial and caudal ends of the articular surfaces of Trochlea carpalis of the Carpometacarpus (Fig. 4.14). With the wrist joint in extension, the edge of the Os carpi radiale fits into the Fovea cranialis ; with the joint flexed the Fovea caudalis accommodates the distal edge of the Os carpi ulnare.

(218) Fossa infratrochlearis. Synonymy: Fossa carpalis intema (Ballmann, 1969a). The depressed area of attachment of the Lig. radiocarpo-metaca.rpale ventrale at the proximal end of the ventral side of the Carpometacarpus. See Fig. 4.14; and Arthr. Fig. 5.5.

(219) Fossa supratrochlearis. Synonymy: Facies ligamentalis extema (Ballmann, 1969a). At the proximal end of the dorsal side of the Carpometacarpus this is the depression for attachment of the dorsal ulnocarpo-metacarpal ligament. See Fig. 4.14; and Arthr. Fig. 5.5.

(220) Proc. pisiformis. Synonymy: Apophysis pisiformis (Lambrecht, 1933). Stubby process of the ventral surface of the proximal end of the Carpometacarpus (Fig. 4.14); serves for attachment of the Retinaculum flexorum, and as a pulley changing the direction of the tendon of M. flexor dlgltorum profundus.

(221) Proc. intermetacarpalis (Milne-Edwards, 1867-71). Synonymy: Tuberositas muscularis (Ballmann, 1969a). This is a process of the major metacarpal bone that projects caudally overlapping, and often fusing with, the dorsum of the minor metacarpal bone (Fig. 4.14); it receives the insertion of M. extensor metacarpi ulnaris. Not present in all birds, it occurs in examples of galli-, pici-, coracii-, and passeriform birds, as well as coliiforms (Ballmann, pers. comm.).

Protuberantia metacarpalis (new term). Synonymy: carpometacarpal process (Harrison, 1968); carpometacarpal protuberance (Feduccia and Olson, 1982). In certain birds the cranial border of the major metacarpal bone bears this hump-like process at about its middle, e.g., in the oscine passerines Menura and Chlamydera (Feduccia and Olson, 1982); in yet other passerines, Progne and Sturnus (pers. obs.), the protuberance is situated farther distally than the above examples.

(222) Symphysis metacarpalis proximalis/distalis (Lambrecht, 1933; Ballmann, 1969a)  The regions of ankylosis of the proximal and distal ends of the major and rrunor metacarpal bones to one another in early postnatal maturation. These so-called "symphyses" are in reality synchondroses which when ankylosed become synostoses. See Arthr. Annot. 129.

(223) Sulcus interosseus. Longitudinal groove on the dorsal aspect of the region of the dIstal metacarpal symphYSIS (Fig. 4.14); the sulcus is occupied by tendons of Mm. interossei.

(224) Ossa digitorum manus. The most common phalangeal formula of birds: one alular phalanx, two phalanges of Digitus major, and one phalanx of Digitus minor. In a number of avian orders the alular digit possesses two phalanges, the terminal phalanx often bearing a claw (hoatzins and turacos, R. W. Storer, pers. comm.); Digitus major often has a third phalanx in anatids (R. W. Storer, pers. comm). See Integ. Annot. 87 for comment on supernumerary digital claws (phalanges); Arthr. Annot. 137.

(225) Pila cranialis phalangis. This is the thickened leading edge of the large proximal phalanx of Digitus major that forms a strong reinforcing bar of bone (Fig.4. 14)" The caudal border of the phalanx is thin and fenestrate in some avian taxa.

(226) Os coxae (Coxa, L hip). Each hip bone is formed by the postnatal ankylosis of Ilium, Ischium, and Pubis. The Pelvis is formed by consolidation of the two hip bones with the synsacrum (see Arthr.).

Acetabulum. The socket in the Os coxae into which the head of the femur fits. Foramen acetabuli. The opening in the floor of the Acetabulum varies in size in different birds. See Arthr. Annot. 151.

(227) Foramen obturatum. This oval-opening situated caudoventral to the Acetabulum transmits the tendon of M. obturatorius medialis and N. obturatorius. The foramen is the detached cranial part of Fenestra ischiopubica (Boas, 1933). See Fig. 4.15; Annot. 252.

(228) Sulcus obturatorius. Long, wide, shallow groove on the medial surface of Ala ischii. M. obturatorius medialis lies in the Sulcus as well as on the adjacent medIal surface of the pubis and Membrana ischiopubica.

(229) Fenestra ischiopubica. Synonymy: Foramen obturatorium, pars caudalis; Foramen oblongum. This gap between the shaft of the pubis and the ischium is of variable shape: from slit-like to elongated oval or triangular; very wide in some forms, e.g., Gavia, Diomedea, Dendrocopus; it is open at its caudal end in Apteryx.

(230) Foramen ilioischiadicum. Situated just caudal to the acetabulum the foramen is bounded dorsally by the ilium and ventrally by the ischium (Fig. 4.15). The foramen transmits the IschiadIic nerves and vessels (Arthr. Mem. ilio. isch.). Generally round or short oval shape; at its caudal end the foramen is incompletely enclosed by bone in tinamous and Apteryx. and extends caudally most of the length of the postacetabular ilium in Rhea, Struthio,  and Casuarius.

(231) Incisura marginis caudalis (Fig 4.9). In lateral view the caudal border of the hip bone (Os coxae) of many birds is indented between Spina dorsolateralis ilii and the tip of Proc. terminalis ischii; this notch is in the region of the ilioischiadic synostosis (see Annot. 230; and Arthr. 148).

Proc. marginis caudalis. Synonymy: Spina iliocaudalis (Boas, 1933). This projection of the caudal margin of the Os coxae of the pelvis between Spina dorsolateralis ilii and the Proc. terminalis ischii is present in some birds (e.g., Gallus, Ardea); not to be confused with the Spina dorsolateralis ilii itself (see Annot. 249). 

(232) Antitrochanter. Located caudodorsal to the Acetabulum, this projection of Os coxae bears an articular surface which is in contact with the neck and trochanter of the Femur; formed mainly by the ischium and to a lesser degree by the ilium.

Sulcus antitrochantericus (Fig. 4.15). Usually a relatively narrow groove dorsal to the Antitrochanter which is the caudal prolongation of the extensive, shallow Fossa iliaca dorsalis of the preacetabular ilium. The sulcus is especially prominent in loons (R. W. Storer, pers. comm).

(233) Crista iliosynsacralis. A median ridge formed by fusion of the right and left dorsal iliac crests with the Crista dorsalis of the synsacrum (see Annot. 143, and below, Annot. 234).

(234) Sulcus iliosynsacralis. In birds in which the dorsal synsacral crest and the dorsal iliac crests remain separate a furrow, the iliosynsacral sulcus, is present on each side of the synsacral crest; the Sulcus contains epaxial muscles. This condition is seen for example in Columba, Ceryle, Corvus.

Canalis iIiosynsacralis (Fig. 4.15). Synonymy: Canalis iliosacralis (Nauk, 1938); subiliac space (Howard, 1929); canalis ilioneuralis (Shufeldt, 1888). Paired can ls occur in the pelvis of birds having an iliosynsacral crest (Annot. 233) (see Komarek, 1979, for illustrations). The paired canals are separated by the dorsal synsacral crest; each is roofed dorsally by the Ala preacetabularis of the ilium; the ventral wall of each canal is the Lamina transversa of the synsacrum (Annot. 141). The canal contains epaxial muscles, occurring, e.g., in Diomedea, Cathanes, Strix, Gallus, Branta, Phoenicopterus.

(235) Concavitas infracristalis. The shallow, wide depression on the lateral surface of the pelvis caudal to the ilioischiadic foramen in many birds; formed largely by the infracristal lamina of the ilium (Annot. 251). The depth of the concavity is exaggerated by the overhanging Crista dorsolateralis ilii (Fig. 4.15). M. ischiofemoralis arises from this surface. Consult Boas (1933).

(236) Pila ilioischiadica. This is the reinforcing pillar of bone along the ventral border of each side of the pelvis extending from the level of the cranial end of the Fossa renalis toward Proc. terminalis ischii. The cranial part of the Pila forms Crista iliaca obliqua (Annot. 242); caudally it contributes to the ventral acetabular wall and ilioischiadic foramen, merging with Ala ischii. See Fig. 4.9.

(237) Fossa renalis (Fig. 4.9). The Fossa renalis is the paired deep fossa on each side of the Corpus synsacri which accommodates the kidney; formed partly by the Synsacrum and partly by the Os coxae (mainly ilium). In general, the cranial division of the kidney is not housed in the fossa, but occupies the shallow depression on the ventral surface of the preacetabular ilium.

Pars ischiadica fossae is the smaller cranial part of the Fossa renalis that contains the middle division of the kidney and the ischiadic (lumbosacral) nerve plexus; the acetabular foramen is an opening in the side of Pars ischiadica.

Pars pudenda fossae is the larger, wider caudal part of the renal fossa that contains the caudal division of the kidney and the pudendal nerve plexus; the ilioischiadic foramen is an opening in the lateral wall of Pars pudenda. See Annot. 250; consult Radu (1975) for comparison of Fossa renalis in galliforms and anseriforms.

(238) Incisura caudalis pelvis. When viewed from its dorsal or ventral aspect, the intact bony pelvis of many birds demonstrates just past its Margo caudalis a wide, semilunar, or rectangular indentation, bounded on each side by the Spina dorsolateralis ilii (Annot. 248). The incisure is notably deep in faiconiform, ciconiiform and strigifurm pelves; its middle part is occupied by the basal part of the free caudal vertebral column; laterally it is completed by the iliocaudal membrane (Arthr. Annot. 185).

(239) Corpus ilii. This is the strongly developed central part of the ilium, cranial and dorsal to the Acetabulum, from which its pre- and postacetabular alae (wings) emanate.

(240) Incisura acetabularis. The body of each of the three elements (ilium, ischium, and pubis) of the Os coxae contributes a segment of the circumference of the acetabulum; each part thus displays a C-shaped Incisura acetabularis. prior to synostosis of the three elements (see Arthr. Annot. 146).

(241) Pila postrenalis. The transverse pillar of bone that strengthens the caudal border of the pudendal part of the renal fossa. Well exemplified in Strix, Larus, and Columba. See Annot. 250.

(242) Crista iliaca obliqua (Boas, 1933). The heavy oblique bar of bone that forms the ventrolateral border of Pars ischiadica of Fossa renalis; the Crista extends between the ventral surface of Ala preacetabularis ilii to the ventral wall of the Acetabulum (see Fig. 4.9; Annot. 236).

(243) Crista iliaca intermedia (Boas, 1933; synsacral strut, Strauch, 1985). Slightly developed in most birds. In some birds this transverse crest is formed on the ventral surface of Ala postacetabularis ilii, within the renal fossa, at the level of the acetabular furamen. The costal process(es) of the so-called true sacral or "acetabular" vertebrae (see Fig. 4.9 and Annot. 141) articulate with the medial end of the crest. The crest is well developed in most charadriifonns (Strauch, 1985); exhibited also, e.g., in Morus, Cathartes, and Columba. See Arthr. Annot. 76.

(244) Tuberculum preacetabulare [Proc. pectinealis]. Synonymy: Proc. preacetabularis; Proc. prepubica. The name, Tuberculum preacetabulare (Boas, 1933), indicates its location at the ventrocranial margin of the acetabulum. It serves as the rear attachment of the Lig. inguinale (Arthr. Annot. 184) which bounds the neurovascular lacuna for the the external iliac vessels and branches of the lumbar nerve plexus. In most birds the Tuberculum is formed by the ilium, in ratites primarily by the pubis (Beddard, 1898). The Thberculum preacetabulare is generally a stubby torus of bone; however, it is an elongated process in Strothio, tinamous, galliforms (Beddard, 1898), and the cuculifurm Geococcyx (Larson, 1930). See Fig. 4.15.

(245) Ala [Pars] preacetabularis ilii; Alii [Pars] postacetabularis ilii. Synonymy: pre-ilium; post-ilium (Parker, 1888).

Crista iliaca dorsalis. Synonymy: Crista iliaca superior (Milne Edwards, 1867-71); Linea iliodorsalis (Lambrecht, 1933). The dorsal (or dorsomedial) border of the preacetabular ilium (see Fig. 4.15 and Annot. 234).

(246) Areae articulares vertebrales. Several areas of the ventral surface of the preacetabular ilium that articulate with the transverse processes of the cranialmost series of synsacral vertebrae. These areas can be seen only in immature birds in which the synsacrum and ilium may be disarticulated (see illustrations in Boas, 1933); most frequently the synsacrum and ilium are ankylosed (synostoses) in mature individuals.

(247) Crista iliaca lateralis (Milne-Edwards, 1867-71). [Margo lateralis] (NAA, 1979). In dorsal view this is the lateral free edge of the preacetabular ilium that in some birds forms a pronounced ledge (Fig. 4.9) (see Annot. 245).

(248) Crista dorsolateralis ilii. Synonymy: Crista dorsolateral is (Boas, 1933); Linea iliolateralis (Lambrecht, 1933); Crista iliaca dorsolateralis (NAA, 1979). Lateral ledge of the postacetabular ilium that marks the boundary between its dorsal and lateral surfaces; indistinct or lacking in some birds, e.g., in the pelecaniforms (Morus, Pelecanus) and anseriforms (Branta, Athyia). The crest serves as an attachment of the aponeurosis of origin of M. iliotibial is (see Fig. 4.15 and Myol. Annot 100).

Spina dorsolateralis ilii. Synonymy: Proc. iliolateralis (Boas, 1933); Spina iliaca dorsalis (NAA, 1979). This is the caudal prolongation of the Crista dorsolateralis ilii (Fig. 4.15). In Columba (Baumel, 1988) the base of the spine forms part of the pulley for change of direction of M. caudofemoralis as the latter enters the lower surface of the uropygium.

(249) Fossa iliocaudalis. This depression on the dorsal surface of the caudal part of the postacetabular ilium on either side of the caudal end of the synsacrum serves as a point of attachment of M. levator caudae (Fig. 4.15).

(250) Recessus caudalis fossae. Synonymy: Recessus iliacus (Boas, 1933); obturator depression (Harvey, et al., 1968). This is the recess of the renal fossa that invaginates the caudalmost junctional region of the postacetabu1ar ilium and ischium. The recess is deep in Gallus and Meleagris, some strigids and gruiforms (e.g., Galinula); it does not enclose part of the kidney, but is fIlled by the origin of M. obturator medialis (Butendieck, 1980). See Fig. 4.9 and Annot. 237.

(251) Lamina infracristalis ilii (Fig. 4.15). Synonymy: Superficies infracrista (Boas, 1933); Lamina ischiadica ilii (NAA, 1979). The vertical lamina of the postacetabular ilium just ventral to Crista dorsolateral is ilii; the lower margin of the Lamina ankyloses with the Ala ischii caudal to the Foramen ilioischiadica (exception: some ratites). See Annot. 235.

(252) Proc. obturatorius (Fig. 4.15). Synonymy: Proc. ventralis. This ventrally directed process of the ischium separates the obturator foramen from the ischiopubic fenestra; formed by ossification of Lig. ischiopubicum.

(253) Proc. terminalis ischii. Synonymy: Proc. terminalis ischiadicus (Boas, 1933); Angulus ischiadicus (Lambrecht, 1933). This process is the most caudal extent of the ischium, often pointed; its lower border articulates with the pubis (Fig. 4.15). See Annot. 231.

(254) Pubis. The shaft (Scapus pubis) of the rather delicate pubis of most birds closely parallels the ventral border of Ala ischii. The two are separated by the obturator foramen and the ischiopubic fenestra (see Fig. 4.15; Annot. 229). In some birds the free ends of the pubes curve inward and closely approximate one another.

(255) Facies articularis antitrochanterica. Synonymy: Articulatio iliacalis (Lambrecht, 1933); Facies glenoidea proximalis (Ballmann, 1969b). Articular surfaces located on the dorsal aspect of the Collum femoris and the medial surface of the Trochanter femoris. See Fig. 4.16; Annot. 232, 262; Arthr. Annot 152.

(256) Trochanter femoris. Synonymy: Trochanter major. On the proximal end of the femur this structure is the elevated, expanded part of the femur continuous with its neck (Annot. 257). Ametov (1971) observed that certain saltatorial birds (e.g., Passer domesticus, Parus major, and Sitta europaea), birds that progress by leaping, lack the femoral trochanter. See Fig. 4.16; Arthr. Annot. 182. Fossa trochanteris. The concavity of the medial surface of the elevated trochanter of the femur; often deepened by the overhang of the Crista trochanteris (e.g., Larus, Gallus, Phoenicopterus).

(257) Impressiones mm. trochanteris; Impressiones ligg. trochanteris (Fig. 4.16). Markings on the lateral aspect of the Trochanter femoris for the obturator and iliotrochanteric muscles and certain ligaments which are detailed by Ballmann (1969b).

(258) Corpus femoris. The body or shaft of the avian femur is commonly circular in cross section; no sharply defined borders are present except in atypical femora (e.g., Gavia) which has a laterally compressed, truncated femur, somewhat quadrate in cross section.

(259) Sulcus patellaris (Fig. 4.16). Synonymy: Fossa patellaris (Lambrecht, 1933); rotular groove (Howard, 1929). Articular groove for the Patella at the distal end of the femur.

Crista lateralis/medialis sulci patellaris. The crests of the patellar sulcus are sharply defined in some taxa.

Condylus medialis; Condylus lateralis. These articular condyles of the distal femur are also known as Condylus internus and Condylus externus. See Annot. 261.

(260) Impressiones ansae m. iliofibularis. Synonymy: impressions of the biceps  loop. The ligamentous ansa (L. loop) for M. iliofibularis has two femoral attachments: one on the caudal surface of the distal femur just proximal to the lateral condyle, the other a distinct scar on the cranial surface of the femur proximal to the lateral crest of the patellar sulcus; a third attachment is the fibula just distal to its neck. See Berger (1966); Myol. Anno!. 102; Arthr. Annot 186.

(261) Trochlea fibularis (Fig. 4.16). Synonymy: Sulcus fibularis. The spool-shaped joint surface on the lateral femoral condyle for articulation with the Caput fibulae. See Arthr. Fig. 5.7.

(262) Crista tibiofibularis (Howard, 1929). Synonymy: Crista peroneo-tibialis (Ballmann. 1969b). Crest on the lateral condyle of the femur that separates its tibial articular surface from that for the fibula; the Crista forms the medial wall of the Trochlea fibularis (see Anno!. 261; and Arthr. Fig. 5.7; Annot. 154). See Fig. 4.16.

(263) Impressio lig. cruciati caudalis/cranialis. The impression for the caudal cruciate ligament is located on the caudal aspect of the distal end of the femur just proximal to the lateral condyle; the impression for the cranial cruciate ligament is farther distal, in the intercondylar sulcus (see Fig. 4.16 and Arthr. Fig. 5.7).

(264) Crista supracondylaris medialis. Synonymy: Adductor crest. This sharp crest extends proxima1ly from the medial condyle of the femur, and is continuous with the caudal intermuscular line of the Corpus femoris (see Fig. 4.16).

(265) Patella. Sesamoid bone in the common tendon of the Mm. femorotibiales and M. iliotibial is. Barnett and Lewis (1958) contend that the elongated patellar crest of some birds (e.g., the common diving petrel Pelecanoides urinatrix) represents fusion of the patella with the patellar crest of the tibiotarsus to which the patellar ligament is attached in most birds (see Annot. 269).

Sulcus [Canalis] m. ambientis. Generally the tendon of M. ambiens perforates or grooves the patellar ligament; in a few birds it perforates or grooves the patella (see Berger, 1966).

(266) Facies articularis medialis/lateralis (Fig. 4.17B). Neither of these articular facets on caput tibiae of the proximal end of the Tibiotarsus is concave; therefore, "cotyla" or "glenoid fossa" are inappropriate; however, well developed intraarticular menisci intervene between the femur and head of the tibia, deepening the surfaces in contact with the femoral condyles (see Arthr. Artcc. genus). The smaller lateral facet faces laterodorsally (see Annol. 262); the larger medial facet lies in a nearly transverse plane.

(267) Facies articularis tibialis. Just distal to its surface for articulation with the femur, the medial surface of the Caput fibulae bears another surface that articulates with the lateral surface (Facies articularis fibularis) of the proximal tibiotarsus. See Fig. 4.17B; Annot. 262, 263; and Arthr. Annot. 157, 159.

(268) Fossa retropatellaris (Fig. 4.17). Synonymy: Fossae synoviales (Ballmann, 1969a); Fossa retrocristalis (NAA, 1979). The retropatellar fossa is situated between the Crista patellaris and the femoral articular facets on the proximal surface of the head of the Tibiotarsus. The Fossa in certain birds appears to be subdivided by a low ridge. In the intact joint the fossa contains the retropatellar fat body (Arthr. Annot. 158). See Ballmann, 1969a.

(269) Crista patellaris (Lambrecht, 1933). Synonymy: Crista rotularis (MilneEdwards, 1867-71; Howard, 1929). Crest connecting the proximal ends of the two cnemial crests of the Tibiotarsus. The patellar crest varies in different birds from transverse to oblique depending on the elevation of the cranial cnemial crest above the articular plane of the head of the tibiotarsus; the Lig. patellae is attached to the crest. See Fig. 4.17; Anno!. 265; and Arthr. Annot. 158.

(270) Crista cnemialis cranialis (Fig. 4.17). Synonymy: Crista cnemial is anterior (Ballmann, 1969a); Crista cnemialis interna or medialis (Cnemial, Gk. tibial). The cranial cnemial crest is elevated well above the level of the knee joint in some aquatic birds (R. W. Storer, pers. comm.) e.g., grebes, herons, flamingos, the diving petrels (Pelecanoididae), and shearwaters (Puffinus); enormously long in the loons. In foot-propelled diving birds the elongation of the crest is associated with shortening of the femur (R. W. Storer, pers. comm.)

(271) Facies gastrocnemialis (Ballmann, 1969a). The medial surface of Crista cnemialis cranialis and the area of the Tibiotarsus caudal to the crest (Fig. 4.17); origin of the medial head of M. gastrocnemius.

(272) Sulcus intercnemialis (Kolda and Komarek, 1958). Synonymy: Sulcus intercristalis (NAA, 1979). Wide longitudinally-oriented sulcus between the cranial and lateral cnemial crests (Fig. 4.17); for origin of M. extensor digitorum longus.

(273) Incisura tibialis (Fig. 4.17). Seen from proximal or lateral view, this is the groove between the caudal surface of the lateral cnemial process and the Facies articularis fibularis of the Tibiotarsus; for passage of the tendon of the Caput femorale of M. tibialis cranialis (Ballmann, 1969a).

(274) Fossa flexoria (Fig. 4.17 A). Synonymy: Fossa flexoris digitorum longi (Ballmann, 1969a). Depression on the caudal aspect of the proximal end of the Tibiotarsus distal to Facies articularis lateralis extending to the proximal edge of the fibular crest; serves as origin for M. flexor digitorum longus.

Tuberositas poplitea (Fig. 4.17). Linear scar on the caudal surface of the tibial shaft just distal to Fossa flexoria; for attachment of M. popliteus (p. Ballmann. pers. comm.). The tuberosity is pronounced in larger birds, e.g., Ardea, Branta, Phoenicopterus.

(275) Corpus tibiotarsi. The proximal two-thirds of the shaft of the Tibiotarsus is for the most part three-sided, with cranial, medial, and caudal surfaces (Ballmann, 1969a).

(276) Linea extensoria (Ballmann, 1969a). The intermuscular line of the cranial surface of the Tibiotarsus is prolonged from Crista cnemialis cranialis along the length of the shaft of the bone; continuous with the medial margin of Sulcus extensorius.

(277) Pons supratendineus (Fig. 4.17D). Synonymy: supratendinal bridge (Howard, 1929); Lig. transversum ossificatum (Lambrecht, 1933). (Pons, L. bridge). The supratendinal bridge is located at the distal end of the cranial surface of the Tibiotarsus proximal to its condyles. The bridge is ligamentous in Bubo, Otus (Berger, 1966), parrots, and ratites (Martin, 1987). See below, Annot. 278.

(278) Canalis extensorius (Fig. 4.17D). The passage deep to the Pons supratendineus at the distal end of the Tibiotarsus that transmits the tendon of M. extensor digitorurn longus. See Arthr. Annot. 164. Tuberositas retinaculi extensoris. Scar at each margin of the Sulcus extensorius of the distal tibiotarsus just proximal to Pons supratendineus (Annot. 277); for attachment of the extensor retinaculum (Arthr. Annot. 187). Since the retinaculum is oriented obliquely the two scars are at different levels.

(279) Trochlea cartilaginis tibialis (Fig. 4.17 A). The trochlea is the wide furrow on the caudal surface of the distal end of the Tibiotarsus, serving as the articular surface for Cartilago tibialis. The sharp Cristae on either side of the trochlea are continuous with the tibiotarsal condyles (see Annot. 280; and Arthr. Annot. 164).

(280) Condylus lateralis/medlalis tibiotarsi. The surfaces of these condyles of the Tibiotarsus that articulate with the Tarsometatarsus face cranially and distally, and caudally are continuous with the crests of the trochlea for the tibial cartilage (see Annot. 279).

(281) Depressio epicondylaris lateralis/medialis. Shallow depression on both lateral and medial sides of the lower end of the tibiotarsus just proximal to the distal articular surfaces of its condyles.

(282) Tuberculum retinaculi m. fibularis [peronei]. On the cranial surface of the distal tibiotarsus the Tuberculum is separated from the proximal part of the lateral condyle by the Sulcus m. fibularis [peronei] (Fig. 4.17C); the tuberculum is the upper point of attachment of the retinaculum which bridges the sulcus and restrains the tendon of M. fibularis brevis in the Sulcus.

(283) Ossa tarsi. The proximal tarsals consist of two elements, the Tibiale [Astragulus] and the Fibulare [Calcaneum], which fuse to each other and to the tibia, producing the condyles of the distal end of the compound bone, the tibiotarsus. "Tibiale" is preferred over Astragalus because in fetal birds there is only one condensation (Cartilago tibiale) that articulates medially with the tibia, whereas the AstraguIus of other amniotes is a compound element composed of additional elements (e.g., intermedium and centralia) that have been lost in birds (Milller and Alberch, 1990). The fibulare does not ossify in most ratites and tinamous; in the exceptions (Struthio and some Dromaius) the cartilaginous lateral condyle ossifies with the tibiale.

The avian ankle is characterized bY an additional element, "Os pretibiale", that McGowan (1985) maintains is associated with the tibiale, whereas Martin and Stewart (1985) associate it with both tibiale and fibulare condensations (although more so with the latter). The pretibiale begins ossifying before either tibiale or fibulare; as a result, it is very unlikely that the pretibiale is homologous to the intermedium of other tetrapods (G. Milller, pers. corom.).

The single distal tarsal bone (Os tarsi distale) fuses with the metatarsals forming the proximal end, including the Hypotarsus, (Annot. 288) of the compound bone, the Tarsometatarsus. Although some workers (see Romanoff, 1960) identified up to four distal tarsals in birds, most recent workers have been able to identify only one (Hinchliffe, 1977; McGowan, 1985; Milller and Alberch, 1990). See Arthr. Annot. 167.

(284) Tarsometatarsus. Metatarsal bones II, III, IV of modem birds ankylose extensively with one another and the distal tarsal bone, forming the definitive Tarsometatarsus. Os metatarsale I is not involved in the ankylosis; instead it has a ligamentous junction with the medial border of the Tarsometatarsus. See Annot. 283; Topog. Annot. 43; and Arthr. Fig. 5.9 & Annot. 167, 173, 174.

(285) Area intercotylaris (Fig. 4.18D). This is the relatively flat area between the plantar parts of the two cotylae of the proximal tarsometatarsus, in other words, the area between the Eminentia intercotylaris and the Hypotarsus. See Arthr. Annot. 171.

(286) Sulcus Iigamentosus. In some birds (e.g., Pelecanus, and the vulture Cathartes) this is a transverse groove at the junction of the proximal Hypotarsus and Area intercotylaris; the ligament from the distal end of Cartilago tibialis is attached in the groove. See Fig. 4.18; and Arthr. Annot. 166.

(287) Arcus extensorius. In certain birds an osseous arch is found on the cranial aspect of the proximal Tarsometatarsus that restrains, and acts as a pulley for, the  tendon of M. extensor digitorum longus (e.g., strigids, picids, rallids, Fulica, Chaetura, et al.) (see Berger, 1966). The arch is in fact the ossified ligamentous Retinaculum extensorium tarsometatarsi of most birds. See Annot. 277, 295; and Arthr. Annot. 188.

(288) Hypotarsus (Fig. 4.18). Synonymy: Calcaneus. This process on the plantar aspect of the proximal Thrsometatarsus is formed mostly by the distal tarsal element (Annot. 283) .capping the proximal end of Os metatarsale m. The Hypotarsus is simple in some birds, consisting of a wide sulcus between low crests (e.g., falconiforms, strigids). In most birds it is complex, having sulci and high crests, and perforated by one or more canals (Newton, 1896). The Sulci and Canales hypotarsi conduct flexor tendons of the pedal digits; consult Berger (1966), Simpson and Cracraft, 1981), and Strauch (1985) for details in different taxa. See Fig. 4.18; Integ. Annot. 68; and Arthr. Fig. 8.

(289) Cristae hypotarsi (Fig. 4.18). Synonymy: Crista externaJinterna hypotarsi (Ballmann, 1969a; Crista ecto-/entogastrocnemialis, (Lambrecht, 1933); calcaneal ridges (Howard, 1929). Lateral, intermediate, and medial crests of hypo tarsus.

(290) Crista medianoplantaris (Fig. 4.18). Synonymy: Crista plantaris (Neugebauer, 1845); Crista plantaris mediana (NAA, 1979); hypotarsal ridge. Median, curved crest that forms a buttress from the middle of the Hypotarsus, gradually merging distally into the plantar shaft of the tarsometatarsus. The tendon of the gastrocnemius muscle extends past its main attachment on the hypotarsus to blend with the superficial border of the Crista (see Annot. 294 and Myol. Annot. 126), creating a se~tum. The septum forms the medial wall of an osseo-fibrous compartment envelopmg the bundle of long flexor tendons for the digits (see Arthr. Annot. 176, Canalis flexorius metatarsi).

(291) Fossa infracotylaris dorsalis (Fig. 4.18A). Synonymy: Depressio antinterossealis (Lambrecht, 1933); Fossa anterior (Ballmann, 1969a). An excavation on the dorsum of the proximal end of the tarsometatarsus immediately distal to its cotylae. The Foramina vascularia proximalia open into the Fossa (Art. Annot. 79); the tuberosity for insertion of M. tibialis cranialis in some birds is situated in the distal part of the Fossa, or m the upper part of Sulcus extensorius of those birds lacking a distinct Fossa.

(292) Facies corporis tarsometatarsi. The surfaces of the shaft of the Thrsometatarsus vary in their configurations in different taxa. In cross section the shaft may be: (1) rectangular, laterally compressed (e.g., Gavia); (2) rectangular, compressed in its dorsoplantar dimension (e.g., Coragyps); (3) triangular, 'Facies plantaris flat (e.g., Ardea); (4) triangular, Facies dorsalis flat (e.g., Pelecanus); U-shaped, concave plantar surface (e.g., Strix) (Annot. 294).

(293) Facies subcutanea lateralis/medialis (Fig. 4.18A). Generally the medial and lateral surfaces (see Annot. 295) of the Tarsometatarsus are covered only with the scaly Podotheca (see Integ). By contrast, the plantar and dorsal surfaces of the Tarsometatarsus have bundles of flexor and extensor tendons interposed between podotheca and bone (Ballmann, 1969a).

(294) Sulcus flexorius (Fig. 4.18C). Synonymy: Sulcus longitudinalis plantaris. In certain birds (e.g., Buteo, Aquila, Strix) the plantar (flexor) surface of the Tarsometatarsus is strongly grooved longitudinally by the Sulcus flexorius which is bounded by the prominent, sharp Crista plantaris medialis and Crista plantaris lateralis (Fig. 4. 18C). The sulcus forms the floor of the Canalis flexorius metatarsi that accommodates the bundle of tendons of the flexor muscles of the digits (Arthr. Annot. 178).

(295) Sulcus extensorius (Fig. 4.18A). Synonymy: Sulcus longitudinalis dorsalis. In some taxa a shallow, longitudinal sulcus indents the dorsal (extensor) surface of the Tarsometatarsus, and contains the intrinsic extensor muscles of the digits (see Annot. 287, 290, 294).

(296) Proc. calcaris (Komarek, 1979). This is the osseous core of the metatarsal spur (Calcar metatarsale). The Proc. calcaris is ankylosed to the medial or caudal aspect-of the tarsometatarsus in males of some galliform birds. See Integ. Annot. 89.

(297) Trochlea accessoria. In piciform, cuculiform, and psittaciform birds the trochlea of the metatarsal bone of the fourth digit possesses an accessory trochlea (Milne-Edwards, 1867-71; Steinbacher, 1935). See Ballmann (1969a) for diagrams of atypical forms of the tarsometatarsal trochleae in several major taxa of birds including those listed above as well as coliiforms.

(298) Canalis interosseus distalis. Synonymy: Canalis m. add. dig. ext. (Lambrecht, 1933). Longitudinally oriented canal that conducts the tendon of M. extensor brevis digiti IV and vessels into the lateral intertrochlear incisure. The upper end of the canal (Fig. 4.18C) is continuous with the Foramen vasculare distaIe (Art. Annot. 79); in some birds the canal is replaced by a groove.

(299) Ossa digitorum pedis. The general avian phalangeal formula is: Hallux, two phalanges; Digitus secundus, three phalanges; Digitus tertius, four phalanges; Digitus quartus, five phalanges. (The hallux is lacking in most ratites). The recommended scheme of numbering the phalanges is that of Berger (1966) and Lucas and Stettenheim (1972). This consists of designating: the most proximal phalanx of a digit as number 1 the next most distal number 2, etc.; in digit IV with five phalanges, the most distal (ungual) phalanx is number 5. The paper of Quinn and Baumel (1990), on the tendon-locking mechanism of the avian foot, follows their scheme. The scheme of Lennerstedt (1975) who designates the ungual phalanx as number 1, the next most proximal phalanx as number 2, etc. is less satisfactory.

(300) Phalanx ungualis. Synonymy: Phalanx terminalis or distalis. This usually claw-shaped phalanx (flattened in grebes, R. W. Storer pers. comm.) forms the bony core of the heavily keratinized claw (Unguis). See Arthr. Annot. 182, 183.

Sulcus neurovascularis (new term). The curved groove on each side of the Corpus of the ungual phalanx that carries nerves and vessels; located just beneath the podotheca of the claw.