Page:The Osteology of the Reptiles.pdf/163

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. 118. Pelves and sacrum: A, Varanus (Lacertilia), from the right. B, Erythrosuchus (Parasuchia), from the right. After Broom. One tenth natural size. C, Rutiodon (Phytosauria), from below. After McGregor. One eighth natural size. D, Nyctosaurus (Pterosauria), sacrum and right innominate bone from within; D′, anterior parasternal ribs of same; D″, prepubis of the same from below.



. 119. Pelves (Therapsida): A, Galechirus (Dromasauria). After Broom. Nearly natural size. B, Diademodon (Cynodontia). After Broom. About one half natural size. C, Galepus (Dromasauria). After Broom. Nearly natural size.

A small opening soon appeared where the four bones meet below in the Theromorpha (Figs. 114, 117), and increased in size, till, in most reptiles, since Triassic times at least, this pubo-ischiatic opening extended on each side nearly to the acetabulum, leaving only a narrow connection between the pubis and ischium (Fig. 118). Later,