The use of the new term "hyolingualis" ("lingual" or "tongue muscles",Richards and Bock,1973) is appropriate and more indicative of the functional role of this musculature in support and movement of the tongue and hyoid apparatus in feeding, food and water transport, and similar related movements (see Zweers,1982).  The use of the alternate term "hypoglossus" is discouraged (see NAA, 1979).

Three or four subgroups of hyolingual musculature are described ( Zweers,1982; Homberger,1986; Homberger and Meyers,1989).  One group, the "external hyolingual muscles " (Annot. 6 and 26 ), consists of superficial [subcutaneous] cervical muscles and "gular" musculature which connects hyolingual elements, other than bones, with nonlingual elements.  These muscles, which typically lie between the tip of the beak and the floor of the pharynx may extend caudally as far as the trachea and pectoral girdle.  They have a major influence on positioning in the floor of the mouth.

A second group, the "extrinsic hyolingual muscles" (Annot. 27, 28, 29, 35, and  37),  connects skeletal elements of the hyoid apparatus with nonhyoidean structures (e.g., mandible, larynx, trachea, clavicle) and directly influences positioning of the lingual apparatus, glottis, and pharyngeal valves.

 A third group, the "intrinsic hyolingual muscles" (Annot. 30 -34), connect two or more elements within the hyolingual apparatus and directly influence positional changes of hyoid elements relative to each other.

See Homberger for illustration of the musculoskeletal attachments (1986, Figs. 12 and 13) as well as Homberger and Meyers (1989) for recent descriptions of laminae and attendant fascial musculoskeletal and/or glandular compartments, associated with the hyolingual apparatus in Psittacus and Gallus, respectively.

(26)  Mm. intermandibulares.  There may be a single muscle, M. intermandibularis ventralis, or two independently developed muscles, M. intermandibularis ventralis and M. intermandibularis dorsalis (dorsal and ventral muscles differentiate by day 12 in development, in Coturnix, McClearn and Noden, 1988).  In either form, the muscle is attached on the medial aspect of Pars caudalis of R. mandibulae and the fibers end in a midventral raphe which may extend from the level of the Rostrum mandibulae (M. intermandibularis ventralis) to the level of Os urohyale of the hyoid apparatus (M. intermandibularis dorsalis).  Both muscles are innervated by R. intermandibularis of N. mandibularis (PNS Annot. 14; see Baumel,1975) which also innervates M. interceratobranchialis (Annot. 30).

 M. intermandibularis ventralis.  Synonymy: M. mylohyoideus (in many studies, see Homberger and Meyers,1989).   M. intermandibularis ventralis is the most superficial and rostral of the two muscles, and the most frequent in occurrence; Fig. 6.7.   Pars rostralis is oriented primarily rostromediad toward a midventral raphe and only the most caudal fibers lie in the transverse plane between the rami of the mandibles.  Pars caudalis is oriented caudomediad toward a midventral raphe and, in many taxa, this raphe becomes continuous with that of M. serpihyoideus or with that of Pars intermandibularis, M. constrictor colli, or both.  It may insert directly on Os urohyale (Osteo. Annot. 81) or on a cartilaginous or bony nodule ("sesamoid plate," Evans,1969, Fig. 5-9; "nodulus," Homberger,1986) which articulates with the hyobranchial skeleton.  Pars rostralis and Pars caudalis may be essentially continuous with one another at the attachment on the mandible.

M. intermandibularis dorsalis.  Synonymy: M. mylohyoideus anterior, "anterior" belly (Mudge,1903); M.hyomandibularis transversus (Kallius,1905); M. suspensor hyoideus (Ghetie and Atanasiu,1962).  M. intermandibularis dorsalis is independently developed in some taxa (Fig. 6.7A; Anser and Anas, Ghetie and Atanasiu,1962; Zweers,1974) but absent in others (e.g., Columba, Zweers,1982).  It is apparently derived from a horizontal splitting of the muscle primordium associated with the mandibular arch (Kallius,1905) and lies dorsocaudal to M. intermandibularis ventralis, in part or entirely covered superficially by the latter.  This dorsal muscle also inserts with its counterpart on a median ventral raphe, separate from that of M. intermandibularis ventralis.

(27)  M. serpihyoideus. Synonymy: M. basibranchialis mandibularis, pars medialis (Vanden Berge,1975; see also Homberger and Meyers,1989).   The origin of the prefix "serpi" is unknown but appears to be derived from the Latin verb "serpo," i.e. "to creep," from which is derived "serpigo," any creeping or serpiginous "eruption" that extends with an arciform border.  In this sense, the prefix may refer to (1) the topographic position of this muscle as it develops by a medial invagination between M. intermandibularis (Annot. 26), M. interceratobranchialis (Annot. 30), and the hyoglossal musculature (Annot. 32 and 33), or (2) its variable proximal attachments (including  Proc. caudalis of the mandible extending medially to include aso Lamina parasphenoidalis in some taxa; see Berger,1966; Richards and Bock,1972, and Burton, 1974, for examples) or (3) its arciform rostral border in some taxa.  In any case, the name has been in common use for many years; Figs. 6.6,7.

    M. serpihyoideus and M. stylohyoideus are innervated by R. hyoideus of N. facialis (PNS Annot. 23; Baumel,1975).  M. serpihyoideus meets the corresponding muscle from the opposite side in a median raphe ventral to the Urohyale, and is functionally related to mechanical support of the gular region, perhaps moreso than direct movement within the hyolingual apparatus, hence it is considered part of the "external hyolingual musculature" (Zweers,1982). 

(28)  M. stylohyoideus. Synonymy: M. basibranchialis mandibularis, pars lateralis (Vanden Berge,1975; see also Homberger and Meyers,1989).  In terms of its embryonic development from the muscle primordium associated with the hyoid arch, Kallius (1905) indicated that it was a homolog of the same muscle in mammals, and that M. stylohyoideus and M. serpihyoideus are innervated by R. hyoideus of N. facialis (PNS Annot. 24; Baumel,1975).  By way of  (1) proximal attachments on the lateral and ventral aspects of Pars caudalis of the mandible, including Proc. retroarticularis if present, and (2) distal attachments on the hyolingual apparatus (Os basihyale), M. stylohyoideus is functionally an "extrinsic hyolingual muscle" (Zweers,1982); Figs. 6.6,7.

(29)  M. branchiomandibularis.  Synonymy:  M. mandibularis epibranchialis (Vanden Berge,1975); M. geniohyoideus (Zweers, 1974; 1982; see also Homberger and Meyers,1989).   A complex muscle in some avian groups (Psittaciformes, Homberger,1986), derived from the muscle primordium associated with the third pharyngeal arch, and innervated by N. glossopharyngeus (PNS Annot. 60).  Pars  rostralis and Pars caudalis are both present in many taxa.  Bhattacharyya (pers. comm.) reports that the attachment on the lateral aspect of the ramus of the mandible, though less common, occurs in a number of passerine as well as non-passerine birds.  Both parts ensheathe the horn of the hyoid on which they insert.

(30)  M. interceratobranchialis [ceratohyoideus]. Considered to be derived from the mandibular muscle primordium (Kallius,1905, but see McClearn and Noden, 1988) although topographically distinctly separated from M. intermandibularis, it is associated primarily with the hyoglossal musculature; see Fig. 6.8.  It is innervated by R. intermandibularis of N. mandibularis (PNS Annot. 14;  Baumel,1975).  Although Zweers (1982) considered the muscle to be part of the functional "external hyolingual musculature," it may be an element of the "intrinsic" musculature, connecting the horns of the hyoid (Cornu branchiale) to each other by way of a ventral midline raphe.

(31)  M.  ceratoglossus.  This muscle connects the Ceratobranchiale with the Paraglossum; see Fig. 6.09B. Homberger (1986) has provided a very complete description of this muscle in the psittacine birds and has given an excellent discussion on the problems of synonymy associated with this muscle; see also Homberger and Meyers (1989).

(32)  M. hyoglossus rostralis [medialis]. Synonymy: M. paraglossobasibranchialis medialis (Vanden Berge,1975); for a complete synonymy, see Homberger and Meyers, 1989.  This intrinsic hyolingual muscle attaches on most of the ventral surface of the Paraglossum and Os basihyale (Osteo. Annot. 80, 81) immediately caudal to the paraglossum.  The terms "rostralis" or "medialis" describe its position relative to M. hyoglossus obliquus (Annot. 33).  See Fig. 6.8 

(33)  M. hyoglossus obliquus [lateralis].  Synonymy: M. paraglossobasibranchialis lateralis (Vanden Berge,1975); for a complete synonymy, see Homberger and Meyers, 1989. The transverse or oblique-transverse orientation of the muscle fasciculi from Os basihyale toward the attachment on the cornua of the paraglossum (Osteo. Annot. 80) is the basis for the term "obliquus" (Fig. 6.8); the adjective, "lateralis," refers to the anatomical position of the muscle relative to M. hyoglossus rostralis [medialis] (Annot. 32).

(34)  M. hyoglossus transversus; M. mesoglossus; M. supraglossus.   These three muscles are considered to be unique to Psittaciformes in which they have been very well described and characterized by Homberger (1986).  She suggests that M. hyoglossus ("hypoglossus") transversus and M. mesoglossus are derived from M. hyoglossus rostralis ("anterior") and that M. supraglossus may have been derived from M. hyoglossus obliquus.

(35)  M. genioglossus [geniopharyngealis, Zweers, 1982].  M. genioglossus has one attachment on Rostrum mandibulae but the other attachment (insertion?) is somewhat variable: (1) on the hyobranchial skeleton or on the fascia of associated muscle, and (2) on the connective tissue underlying the oral mucosa lateral to the tongue (Bock et al., 1973).  Occasionally, the insertion is said to extend as far  caudally as the cricoid cartilage.  The muscle is considered a protractor of the hyolingual apparatus and part of the "external hyolingual musculature" (Zweers,1982).  It is absent in Gallus (Homberger and Meyers,1989), at least in the adult, but is said to be present in fetal development (Noden, 1983).

(36)  M. cricohyoideus dorsalis; M. cricohyoideus ventralis. These two muscles connect Os basihyale with Cartilago cricoidea.  With M. hyovalvularis and M. tracheovalvularis, they form the principal musculature of the avian oropharynx,  integrated into the functional apparatus directly governing movements of the "ventral pharyngeal valves" and "pharyngeal scrapers", independent from lingual, glottal and beak movements (Columba, Zweers,1982; Zweers and Berkhoudt,1987; Heidweiller and Zweers,1990).  All four muscles are more fully described in Resp. Annot. 45, and Figs. 8.