PELVIC ARCH 



117 



greater development of the ilium, which is sometimes broadened 

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

 tion of the arch as a whole. 



Points of connection with the pelvis of Amphibians are seen in 

 Paleeohatteria, the Plesiosauria, Hatteria, Telerpeton, and the 

 Chelonia (comp. Figs. 93 and 94), while the pelvis of the Ichthyo- 

 sauria approaches that of the Lacertilia. In the latter, and still 

 more in the Crocodilia and Dinosauria, the pelvic arcli is much 



Fig. 95.— A, Longitudinal Horizontal Section thkough the Ventral Part 

 OF the Pelvis of an Embryo of Lacerta agilis, 32 mm. in Length. B, 

 Pelvis of Lacerta vivipara. (From the ventral side. ) 



Ep, epidermis ; P, pubis ; PP, prepubis ; Is, ischium, forming a symphysis at 

 Sis ■ Hpis hypoisohium, which becomes segmented off from the hmder ends 

 of the isohia in the embryo as a paired structure ; f, dense mass of embryonic 

 tissue ; /, ilium, with its small preacetabular process tt, which is much 

 more strongly developed in Crocodiles, Binosaurians and Birds ; Ac, aceta- 

 bulum, in which the three pelvic bones unite together so that the sutures 

 between them become obliterated ; Fo^, obturator foramen ; Gep, epipubis, 

 composed of calcified cartilage ; Lg, fibrous ligament. 



more highly differentiated; while in Snakes, on the other hand, it, 

 like the pectoral arch, is entirely wanting. 



In Hatteria (Fig. 93 E) there is a marked epipubis and a hypo- 

 ischiatic process continuous with the epipubic cartilage, and the 

 prepubic processes are strongly developed. The obturator and 

 ischiopubic foramina are distinct from one another, and not united 

 into one, as in Chelonia. (For the various modifications seen m 

 the pelvis of the latter Order, more particularly as regards the 

 relative development of the epipubic and prepubic processes and 

 the relations of the ischium and pubis, compare Fig. 94.) 



