294 INEZ L. WHIPPLE. 



muscles does not however as in the case of Necturus preclude 

 the possibility of descent by degeneration from some higher 

 lunged form, since the entire pelvic region shows numerous signs 

 of degeneracy. 



With regard to Typhlomolge, Miss Emerson (1905) has already 

 shown conclusively the probability that this form is a permanent 

 larva of a lungless salamander. Unfortunately I have not at 

 hand the means for ascertaining whether in this form, as in the 

 known Plethodontidte, vestiges of ypsiloid muscles occur, but 

 Miss Emerson mentions the failure of the cartilage as one of the 

 characteristics of Typhlomolge. My proof that the use of the 

 ypsiloid cartilage is correlated with the hydrostatic function of the 

 lungs, therefore merely strengthens Miss Emerson's argument 

 that Typhlomolge is the larva of a lungless form. 



In conclusion, I wish to acknowledge my indebtedness to Dr. 

 Harris H. Wilder for much practical assistance in the preparation 

 of this paper. 



SUMMARY. 



1. The ypsiloid apparatus is, with the exception of Crypto- 

 branchus, confined to the suborder Salamandrida. It has arisen 

 in response to the physical need of controlling the direction of the 

 body in water through the adjustment of the relative buoyancy 

 of the anterior and posterior ends. Its function is therefore 

 closely correlated with the hydrostatic function of the lungs. 



2. In origin the ypsiloid cartilage is independent of the pelvic 

 girdle. Its stem arises as a chondrification of the linea alba of 



o 



the somite immediately anterior to the pelvic girdle. The arms 

 are more complex in origin since the process of chondrification 

 involves not only the myocomma anterior to the above named 

 somite but also the outer edge of the aponeurosis of the trans- 

 versalis muscle. 



The Cartilage ypsiloides is therefore not homologous either 

 with the Proccssns epipubicits of the lower Urodelcs or with the 

 marsupial bones of certain mammals. 



3. In the Plctliodontidce and Desmognathidce, in which the 

 lungs have wholly degenerated, a correspondingly complete 

 degeneration of the ypsiloid cartilage has occurred, although 



