SKELETON 



119 



pelvic 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. 63). In the interpretation of some of the 

 pelvic elements there is some uncertainty. 



In the stegocephals (fig. 125) ischium and 

 ilium (and usually pubis) were distinct bones 

 with apparently considerable cartilage be- 



FiG. 126. 

 il, ilium; is, ischium; p, pubis. 



Fig. 125. 



Fig. 1 25. — Pelvis of Discosaurus, after Credner. 



Fig. 126. — Ventral view of pelvis and ypsiloid cartilage of Cryptohranchus, after 

 Wiedersheim. a, acetabulum; tl, ilium; is, ischium; a, obturator foramen; p, con- 

 joined pubes; y, ypsiloid cartilage. 



tween them. In 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 indistin- 

 guishably 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 

 pubic. An interesting feature is furnished by the ypsiloid cartilage 

 (fig. 126) 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 



