706 COMPARATIVE ANATOMY 



formed independently of the pubis, in the linea alba,. called the ypsiloid 

 cartilage. 



In the frog and other anura, the three pelvic bones are present, all 

 of which participate in the forming of the acetabulum, although the ilium 

 is very long and the ischio-pubis strongly compressed, so that the ob- 

 turator foramen and ischio-pubic fenestra are absent. 



In reptiles, the pelvic bones are more solid and distinct than in any 

 of the lower forms. The ilium is often expanded, the ischio-pubic fenes- 

 tra large, and the ischium and pubis united from side to side by an epi- 

 pubic cartilage or a modification of this, known as the ligamentum me- 

 dium pelvis. 



In some turtles, the epipubic cartilage bounds the fenestra on the 

 median side, but in all turtles, the fenestra and the obturator foramen 

 are merged into one. In lizards, there may be a separate bone ossified 

 from the posterior part of the epipubis. This bone is called the os cloacae 

 or hypo-ischium. 



In legless lizards, the pelvis is greatly reduced, while all trace of it 

 is lost in the snakes, except the boas, and some opoterodonts (worm-like 

 serpents). In the crocodiles, due to the oblique position of the pubes, 

 the obturator foramen is very large. The pubes themselves do not unite 

 with each other. There are cartilaginous tips on the medial end which 

 may be separate epipubes. The lower end of the ilium also separates 

 as a distinct bone. 



It is interesting to note that the pelvis of Dinosaurs has the ilium 

 arranged quite similar to that in birds. The sacrum also is somewhat 

 similar, due, apparently, to the upright position in which these animals 

 walked. The ischia are elongated, extending backward, and often uniting 

 below, while the pubic bones extend forward and downward, and have 

 strong post-pubic processes running parallel to the ischium, while often 

 the ilium gives off an iliac spine near the acetabulum. 



The Pteryodactyls also had elongated ilia, similar to the Dinosaurs. 

 The ischium was then fused with the ilium, so that the pubis took no 

 part in the forming of the acetabulum. In these the pelvic opening was 

 very small. 



In birds of the present time, the pelvic bones are fused ; the ilium is 

 quite long, and usually fused with the synsacrum, while the ischium and 

 pubis extend backward. 



The pubes lie in the position of the postpubes of Dinosaurs, and 

 never meet below, except in ostriches. However, in the embryo, the 

 pubes run forward, only gaining their final position later on. There is 

 a pectineal process which arises in the acetabular region and extends 

 forward, quite like the pubis in Dinosaurs. In the mammals, the obtura- 



