4: OSTEOLOGIA

JULIAN J. BAUMEL and LAWRENCE M. WITMER

With contributions from subcommittee members: P. Ballmann, D. Hogg, V. Komarek, R. Landolt, R. J. Raikow, E. I. Saiff, R. W. Storer, J. C. Vanden Berge, R. L. Zusi, O. Zweers.

Among contemporary workers in avian osteology, Peter BaIlmann for years has been concerned with standardization of anatomical terminology. His scholarly and painstaking assistance in the compilation of the postcranial osteological terminology is most commendable. In the first and second editions of Nomina Anatomica (NAA, 1979) R. L. Zusi, J. Vanden Berge, and R. Landolt have made important contributions in codifying the nomenclature of the skull and vertebral column. The dissertation of Butendieck (1980) provided a worthy review and critique of the osteology terminology of the NAA (1979). The highly detailed nomenclature of the skeleton of birds presented here will be particularly useful to avian paleontologists, myologists,arthrologists, and systematists who use osteological characters. In the compilation of terms the major works most heavily drawn upon were those of Furbringer (1888), Lambrecht (1933), and BaIlmann (1969a) for the limb bones; Barkow (1856), Boas (1929, 1933), Komarek (1970, 1979), Landolt and Zweers (1985), and Zweers, et al. (1987) for the vertebral column; Hofer (1945, 1949, 1955) and Miiller (1963) for the skull.

Nomenclature of digits of wing. The matter of homologies of the digits of the avian thoracic limb has long been a debatable point among avian morphologists. There is still no indisputable evidence for deciding if the elements of the avian manus represent digits I, IT, ill or IT, ill, IV. Berger (1966) summarized the controversy on. the subject, citing the principal literature up to that time. Seichert and Rychter (1972) discussed and further reviewed the literature on this topic. Recently Hinchliffe (1985) and Muller and Alberch (1990), using more precise techniques than the older embryo-staining methods, have determined that the persisting digits in one species of modern birds  (chicken) are II, ill, and IV. On the other hand, most.workers regard birds as derivatives of theropod dinosaurs; in these dinosaurs, the evolutionary sequence clearly points to the presence of digits I-II-ill as being the components of the tridactyl manus (Ostrom, 1976). Thus the problem is still unresolved.

Rather than perpetuate names of the skeleton and musculature of the manus based on the controversial numbering of the digits by arbitrarily choosing one of the systems in use, an alternative, less equivocal scheme was adopted in the first edition of the NAA (1979): P. Brodkorb originally suggested reviving the proposal of Milne-Edwards (1867-71), designating the digits and their skeletal elements by the descriptive names: Digitus alularis (the sO<alled pollex), Digitus major, and Digitus minor; Os metacarpale alulare, Os metacarpale majus, and Os metacarpale minus. This terminology has been well accepted, and continues in the present edition. See Annot. 214 and Myol. Intro. Format for listing tenns. The skeletal parts that are listed and described are mostly those of ¢e dried bones of mature individuals from which the cartilaginous and ligamentous structures have been removed. Most of the anatomical names for skeletal features are listed under the name of the individual bone of which they are parts. For example, Foramen n. ophthalmici and Proc. postorbitalis are parts of Os laterosphenoidale. On the other hand, numerous features of the skull, pelvis, and vertebral column are not limited to a single bone, but extend over two or more different, adjacent bones (e.g., crests, fissures, fossae, etc.). Extensive fusion of individual bones of the adult avian skeleton often makes it difficult or impossible to identify adjacent bones from one another; however, many of them can be readily distinguished in immature skeletons.

Names of such compound shared features in the mature skull involving more than one bone are listed under the headings Facies and Cranium; subheadings are Cavum nasi, Orbita, Cavum tympanicum, Cavitas cranialis, and Mandibula. In the adult skull features confined to individual bones are to be found under the headings: Ossa faciei and Ossa cranii; in some instances the same term may be listed in more than one place. In the postcranial skeleton, other complexes of shared elements are: the Notarium and Synsacrum (parts of Columna vertebralis), the Carpometacarpus, Os coxae, Tibiotarsus; and Tarsometatarsus; these receive treatment similar to that of Facies and Cranium.

TERMINOLOGY

TERMINI GENERALES

Aditus

Ala

Angulus

Anulus [Annulus]

Antrum

Apertura