PELVIC ARCH 



149 



a long rod (Fig. 108, c) ; and the ischiopubic plate, which in 

 Urodeles lies in the plane of the abdominal walls, becomes closely 

 pressed together in the middle line and gives rise to a well-marked 

 ventral keel : it is not perforated by the obturator nerve. The 

 pubic region, moreover, though often calcined, is independently 

 ossified only in the case of Xenopus (Fig. 108, A, B). 



Reptiles. The chief characteristics of the Reptilian pelvis as 

 compared with that of Amphibians consist in : (1) a much more 

 marked differentiation of the pubis, which is more distinctly 

 separated from the ischium by an ischiopubic foramen; (2) the 

 greater development of the ilium, which is sometimes broadened 

 out at its vertebral end; and (3) the more intense and solid 

 ossification of the arch as a whole. 



Points of connection with the pelvis of Amphibians are seen 

 in certain fossil forms (e.g. Palseohatteria, Plesiosauria), and also 



FIG. 109. PELVIC ARCH OF Hatteria. (After Credner.) From the 

 ventral side. 



Ctp. epipubic cartilage ; Fo l , obturator foramen ; /, ilium ; Is, ischium ; P, 

 pubis ; pp, prepubis ; *, hypoischiatic process, which becomes segmented 

 off from the pelvis in other Reptiles, t, t, ischiopubic foramina. 



in Hatteria and the Chelonia. In the Plesiosauria and Hatteria 

 (Fig. 109) the pubes are not very widely separated from the 

 ischia, so that the ischiopubic foramina are not so extensive as in 

 many other Reptiles. 



From this condition that seen in the Chelonia, more especially 

 in Macrochelys and Chelydra, maybe easily derived (Fig. 110, A). 

 In both cases the epipubis and prepubis are strongly marked. In 

 other respects there is great variation in the form of the pelvis in 

 Chelonians, but the obturator and ischiopubic foramina are never 

 distinct from one another (Fig. 110). 



The pelvis of the typical Lacertilia (Fig. Ill) is characterised by 



