| OCR Text |
Show 1893.] OF T H E TERRESTRIAL VERTEBRATA. 587 portion of the coracoidal skeleton not involved in the clavicular apparatus, and to its homologue the term coracoid is applied in all the lower Vertebrata, whether it be ossified or not. What, then, are we to term this, if Mr. Lydekker's system is to endure ? The context of his paper suggests coracoido-metacoracoid as a likely term; but before that could be introduced it ought to be shown that the single ' coracoid' of living Lizards, which is coincident in area with the conjoint coracoidal elements of Anomodonts and Mammals, is the product of fusion of these. No one has yet demonstrated the remotest trace of more than a single centre of ossification in the Lacertilian coracoid; while, on the other hand, its double ossification in the Mammalia, in its non-abbreviated form (Ornithorhynchus), is preceded by its segmentation while still cartilaginous. Mr. Lydekker's proposals might perhaps be accepted were the Mammalia and Anomodontia alone concerned. Anatomical terminology, however, unlike nomenclature in systematics, must needs be applicable to all classes of this or that sub-kingdom ; and it has therefore to cover a very wide range of structural variation. These considerations, together with those which I have already raised, appear to m e fatal to the acceptation of Mr. Lydekker's terms, which seem no more tenable than the application of the human anatomists' term 'scapula' to the coraco-scapular 'blade-bone,' into which he lapses in his final footnote on p. 174, and which, on grounds of sheer priority, should be adhered to. W e are dealing with a common (coracoidal) cartilage, which is in some animals replaced by a couple of osseous elements, and in others by but one. Setting aside the precoracoid and clavicle, the ultimate homologies of which are by no means yet fully worked out, our present requirements may be met by the retention of the universal term coracoid for the entire set of structures (i.e. the cartilaginous 'coracoid' bar and its derivatives), with the introduction of, say, the terms unicoracoidal and bicoracoidal for its diversely modified types, and the retention of Cuvier's epicoracoid for its anterior and Lydekker's metacoracoid for its posterior segment in the latter one. Upon this basis, the sum of our knowledge of the coracoid of Amphibia and Amniota may be formulated as follows :- Coracoid. i. unicoracoidal. Amphibia, all living Reptilia, Aves. ii. bicoracoidal. Some Anomodontia, Mammalia, Ich-thyosauria and Nothosauria (?). A simple alternative would be the description of the common coracoid as either uni- or bi-segmented ; but this, for obvious reasons, would be insufficient. The arrangement which I here propose admits of the retention of the human anatomists'' term 'coracoid process' as all-sufficient for the requirements _ of the systematic mammalogist, who, except for his concern with the Monotremes, deals with the vexed element only in its most abbreviated and vestigial conditions. |
