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COMPARATIVE MORPHOLOGY OF VERTEBRATES 



habits the ilium is very long and the ischio-pubis is strongly com- 

 pressed, obturator foramen and ischio-pubic fenestra being absent. 

 Omitting the extinct rhynchocephals, whose pelvis resembles 

 that of the stegocephals, the reptiles have the pelvic bones more 

 solid and distinct than do the ichthyopsida; the ilium is strong, with 

 its dorsal end frequently expanded; the ischio-pubic fenestra is 

 large; and ischium and pubis are united to their fellows directly, 

 or by the intervention of the epipubic cartilage, or its modification, 

 the ligamentum medium pelvis. As a rule all three bones meet in 

 the acetabulum and there are large prepubic processes, though these 

 are small in the lizards and are lacking in crocodiles. 



Fig. 127. Fig. 128. 



Fig. 127. — Pelvis of snapping turtle {Chelydra) from below, e, epibubis;/, femur; 

 A, hypoischium; i. ischium; /, ligamentum medium pelvis; p, pubis; pp, pectineal process. 



FiG- 128. — Pelvis of Iguana tuberculata, after Blanchard. a, acetabulum; e, 

 epipubic cartilage;/, femur; II, ilium; is, ischium; of, obturator foramen; p, pubis; pp, 

 prepubis; s,^ s^, first and second sacral vertebra;. 



Many theriomorphs have the pelvic bones fused much as in 

 mammals. In Sphenodon and some turtles the epipubic cartilage 

 bounds the fenestra on the median side, and Sphenodon and the 

 plesiosaurs have a separate obturator foramen, but the two are 

 merged in the chelonians. Most lizards have slender pubic bones, 

 perforated by the foramen, and the part of the epipubis between the 

 fenestras reduced to a ligament, while the posterior part of this, behind 

 the ischium, may ossify as a distinct bone (os cloacae or hypoischiimi) . 

 In the footless lizards the pelvis is reduced, being represented in the 

 amphisbaenans by rudiments of ischium and pubis, while all traces 

 of the pelvis are lost in snakes, except the boas and some opoterodonts. 

 The obturator foramen is very large in the crocodiles, the result of the 

 oblique position of the pubes, which do not unite with each other; 

 each is tipped with cartilage (? separate epipubes). All three bones 



