274 INEZ L - WHIPPLE. 



to study either the anatomy or the habits of Dactyletra in which 

 an apparently similar cartilage to the Cartilago ypsiloides is formed, 

 and can therefore express no opinion as to this homology. 



That the Cartilago ypsiloides of salamanders is homologous 

 with the marsupial bones of Monotremata and Marsupulia is a 

 view which has been considered so completely established that 

 Duges ('55) named this cartilage in salamanders the "marsupial 

 cartilage." Huxley also accepted this idea of its homology and 

 it is one of the principal points made by Wiedersheim ('92) in his 

 Phylogenie der Beutelknochen, in which, of course, this interpre- 

 tation is quite consistent with his idea that both the ypsiloid 

 cartilage and the marsupial bones are differentiations of the epi- 

 pubic process. Moreover, the acceptance of this homology is 

 indicated in the various names which have been given to the M. 

 ypsiloidcus posterior, such as pyramidalis (Hoffmann). Leaving out 

 of account the question as to whether the ypsiloid cartilage and 

 marsupial bones are of similar origin so far as the pelvic girdle 

 is concerned, the supposed homology between the two is dis- 

 proved by their relations to the rectus abdominis muscle. The 

 ypsiloid cartilage lies dorsal to the main mass of this muscle ; 

 the marsupial bones are, of course, ventral to it. A comparison 

 of musculature, therefore, shows the lack of homology of the 

 ypsiloid apparatus with the marsupial. The musculature of the 

 ypsiloid cartilage is derived from the deeper layers of the rectus 

 abdominis and from the transversalis ; from the very poistion of 

 the marsupial bones, on the other hand, it is evident that the 

 musculature of this apparatus is derived from the superficial ab- 

 dominal muscles. 



The pyramidalis, which has been homologized with the M. 

 ypsiloideus posterior is, for example, the most superficial portion 

 of the rectus abdominis. Further, it is on the wrong side of the 

 marsupial bone to make the homology a consistent one through- 

 out, since, if the marsupial bones correspond to the lateral arms 

 of the Cartilago ypsiloides, a muscle to be the homologue of the 

 M. ypsiloideus posterior must extend from the outer edge of the 

 marsupial bone to the pelvis, not as does the pyramidalis, from its 

 medial side to the linea alba or sternum. The pyramidalis and 

 the posterior ypsiloid muscle are then homologous only in the 



