PELVIC GIRDLE — REPTILIA 



263 



cartilage do not surround, but lie in front of the obturator nerve so 

 that no foramen is formed. Occasionally there is an ossification of 

 an OS pubis (Aglossa). A third difference is the great elongation of 

 the ilium which connects with a single sacral vertebra (in one or two 



Fig. 280. — Pelvis of Necturus (Wilder, '03). a, acetabulum; e, epipubis; il, ilium; 

 is, ischium; sr, sacral rib; 18-20, vertebrae. Bones lined, cartilage stippled. 



fossils two sacrals are described). The acetabulum is a cup, bounded 

 by ossified ischium and ilium, a cartilage (probably pubic) lying on 

 its lower anterior side. The acetabular region is very short, laterally 

 compressed, and forms a plate in the median 

 hne, the two acetabula being separated by 

 cartilage. In Aglossa the two sides are dis- 

 tinct, the region less compressed and, besides 

 a pubis, an epipubis is present. 



Fig. 281. Fig. 282. 



Fig. 281. — Pelvis (ventral side) of Cryptobranchiis (Wiedersheim). a, acetabulum; 

 il, ilium; is, ischium; o, obturator foramen; p, pubic cartilage; y, ypsiloid cartilage. 

 Fig. 282. — Pelvis of frog, a, acetabulum; il, ilium; is, ischium; p, pubic? cartilage. 



REPTILIA. — Where development is known, the reptilian 

 pelvis arises from a pair of cartilages, each with a large gap on the 



