no 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



fins so that they come to lie in front of the pectorals (the old group 

 of 'jugulares'). 



The elasmobranchs have a true girdle, but without separate ele- 

 ments as it does not pass beyond the cartilage stage. It consists of a 

 continuous ischio-pubic bar, extending from one acetabulum to the 

 other, and usually prolonged dorsally above the acetabulum by an 

 iliac process. 



In all fishes the pelvic girdle is free from the vertebral column, but 

 in the tetrapoda, where the limbs have to support the body weight, the 

 girdle becomes connected with the sacrum by 

 the intervention of one or more sacral ribs (p. 

 56). In the interpretation of some of the 

 pelvic elements there is some uncertainty. 



In the stegocephals ischium and ilium and 

 usually pubis were distinct bones with appar- 

 ently considerable cartilage between them. In 



FIG. 114. FIG. 115. 



FIG. 114. Pelvis of Discosaurus, after Credner. U, ilium; is, ischium; p, pubis. 



FIG. 115. Ventral view of pelvis and ypsiloid cartilage of Cryptobranchus, after Wieder 

 sheim. a, acetabulum; il, ilium; is, ischium; o, obturator foramen; p, conjoined pubes; 

 y, ypsiloid cartilage. 



the urodeles the two ischio-pubic cartilages are usually united in the 

 median line, but the ossifications vary in extent, the pubic region lagging 

 behind the ischium and being at times indistinguishably fused with it. 

 In some cases there is, as in Necturus, an extension of the median 

 cartilage forward in an epipubic process, and frequently a pectineal 

 process from the antero-lateral of each pubis. An interesting feature 

 is furnished by the ypsiloid cartilage (fig. 115) formed independently 

 of the pubis and extending forward in the linea alba through two or 

 three somites. This occurs only in salamanders with functional lungs, 

 where it furnishes attachment for muscles connected with respiration. 

 In the anura all three pelvic bones are present, and all participate in 

 the formation of the acetabulum. Correlated with the leaping habits 



