ON THE EPISTEENAL APPAEATUS OF MAMMALS. 561 



Erom a consideration of the foregoing statements no reasonable 

 doubt can be entertained that in the interarticular fibre- cartilage 

 which separates the clavicle from the sternum, we have the equiva- 

 lent of the symmetrical episternals. In Cercopithecus (0. ruber) 

 I find a general agreement in the composition of the sternoclavicular 

 articulation with that of man ; the interarticular fibro-cartilage, how- 

 ever, being a good deal thicker behind, so that when viewed on that 

 aspect it at once strikes the eye as being an independent structure. 

 Here also, as in man, the presence of the cartilage causes the joint 

 to be composed of two chambers or cavities. In order more easily 

 to explain the structure of the sternoclavicular articulation, and at 

 the same time to serve as a means of comparison, I have made a 

 drawing of a somewhat oblique vertical section of it, and the inter- 

 articular fibro-cartilage may be seen to form a distinct portion of the 

 skeleton, both in man and apes ; whilst not only from its general 

 relations, but also through its intimate connection with the sternal 

 end of the clavicle and with the manubrium sterni, it is obviously to 

 be regarded as a peculiar modification of the episternal piece, though 

 certainly less developed than even in the Cheiroptera. The epi- 

 sternals are consequently portions of the shoulder girdle, which only 

 vanish entirely when the clavicles are wholly absent, but which are 

 always visible when the clavicles are present, and frequently form 

 structures of very considerable magnitude. Now if we regard the 

 interarticular fibro-cartilage of the sterno- clavicular articulation as 

 the representative of the episternals, it follows that the occasionally 

 present " ossa supra- sternalia " described by various authors, and 

 recently in particular by Luschka,* as sometimes occurring in man, 

 must be considered to hold an intimate relation to the typical epi- 

 sternals of armadillos, &c. But a comparison of these ossifications 

 lying in front of the manubrium sterni with the episternals of the 

 armadillos, &c., is by no means satisfactory when we know that 

 certain constantly present portions of the skeleton, namely the 

 interarticular fibro- cartilages have already been determined to be 

 the equivalents of the symmetrical episternals. Nevertheless I am 

 unable at once to explain away these oasa supra-sternalia by consider- 

 ing them as merely accidentally and rarely occurring structures ; for 

 it is possible they may stand in genetic connection, not indeed with 

 the more commonly developed symmetrical wings, but with the pro- 



* Zcitschrift fur wisscaschaft. Zoologie. Bd. iv. p. 36. 



