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Show 1893.] ON THE CORACOID OF THE TERRESTRIAL VERTEBRATA. 585 7. On the Coracoid of the Terrestrial Vertebrata. By G. B. H O W E S , F.Z.S., F.L.S., Assistant Professor of Zoology, Roy. Coll. Sci. Lond. [Received June 20, 1893.] I. As to Terminologg. It is now generally conceded that some of the Anomodont reptiles, which in many respects so closely approximate towards the Mammalia in their skeletal anatomy, were possessed of an expanded epicoracoid of the Monotreme type. Professor Seeley, to whom we are chiefly indebted for the discoveries which have rendered this conclusion clear, discards the Cuvierian term " epicoracoid " and persistently applies the term precoracoid to the element in question in both reptiles and mammals 1. In this he is followed by Mr. Hulke2. Mr. Lydekker, however, in a recent communication to this Society 3, has proposed to abolish the term epicoracoid altogether, in association with a discovery of m y own4 that the element to which in the Monotreme the term ' epicoracoid ' was first applied is the serial homologue of the coracoid process of the higher mammals, to which, in the long run, the term ' coracoid' was originally given. Tbe term precoracoid (procoracoid of Gegenbaur) is well known to be used in two or more totally distinct senses (sometimes by the same observer in the same paper 3). It is for the most part either applied to a mere process of the coracoid, most variable in its relationships when present and in no sense originally distinct, or restricted to that bar which underlies the clavicle6 and (some ' Cf. Phil. Trans. 1888, B. pp. 490-492, 1889, B. pp. 255 and 275, and P. R. S. vol. Ii. p. 119. 2 P. R. S. vol. Ii. p. 233. 3 See P. Z. S. 1893, p. 172. 4 Journ. Anat. & Phys. vol xxi. p. 192. 3 Cf. Hulke, loc cit. description of figs. 4, 6, 7, and 9. 6 Goette, as is well known, confirmed Rathke's discovery of this " Anlage " in the young lizard. The contradictory argument s which have been based upon its supposed distinctness or non-distinctness in this or that animal lose their force to-day in the tendency of recent research to demonstrate, more and more clearly, that the three great elements of both the pectoral and pelvic girdles are at first independently differentiated. (Cf. especially the papers of Miss Lindsay in P. Z. S. 1885, p. (192, and of Mehnert in Morph. Jahrb. Bd. xiii. p. 293, & Bd. xv. p. 110). There can, I think, be little doubt that the Rathke-Parker conclusion that the dermo-clavicular elements are in the Chelonia represented by theecto-andento-plastra is correct. It appears to me highly probable that in these animals the claviculo-coracoid apparatus has undergone a kind of analysis into its constituent elements, and that the precoracoid (in the non-differentiation of a distinct endosteal centre within its substance, such as Gegenbaur first described for man himself) has become ossified by an extension of the acromial tract. Baur has lately proposed to term this apparent acromion a ' proscapula' (cf. Proc. Acad. Nat. Sci. Philad. 1891, p. 424), a by no means inappropriate term, if a new one be necessary. |
