142 THE OSTEOLOGY OF THE REPTn.ES 



more elongated, in bipedal forms slender. The scapula of the Cotylo- 

 sauria (Figs. 95, 96, b, c) is relatively short and broad; that of the 

 Theromorpha (Figs. 98, 106) more elongated, but never narrow; that 

 of the therapsid reptiles (Fig. 107) relatively narrow, slender in the 

 Dromasauria. The scapula of the Sauropoda (Fig. 113 d) is rela- 

 tively long, that of the Predentata (Fig. 1 13 c) is much more slender, 

 but it is most slender and bird-like of all in the Theropoda (Fig. 



113 A, b). The scapula of the Pterosauria (Fig. 109) is always elon- 

 gated, very slender and bird-like in some of the earlier forms, but 

 stouter and firmly fused with the coracoid in the latest. In the most 

 specialized of all pterodactyls (Pleranodon, Ornithocheirus) its en- 

 larged distal extremity articulates with the fused spines of the dorsal 

 vertebrae, the only known examples among vertebrates of the articu- 

 lar union of the pectoral girdle with the spinal column. 



In the early reptiles the scapula was more nearly erect, or with 

 a slight inclination backward. In the Crocodilia, Pterosauria, and 

 bipedal ,reptiles, as also birds especially, it is very obliquely placed,, 

 the upper end turned backward over the ribs. 



The Pelvic or Hip Girdle 

 (Figs, i 14-127) 



The pelvic girdle or pelvis, in reptiles, as in other air-breathing ver- 

 tebrates, is composed of three bones on each side, more or less firmly 

 coossified in the adult, and collectively known as the innominate; the 

 girdle is completed by the sacrum on the dorsal side with which the 

 pelvis is never closely united in reptiles, not even in the Pterosauria. 

 The upper or dorsal bone of the three, that to which the sacral ribs or 

 transverse process of the lumbar vertebra are attached, is the ilium; 

 the one on the lower or ventral side in front is the pubis; that on the 

 ventral side behind is the ischium. On the outer side, where the 

 three bones meet, there is a cup-like depression, sometimes a hole, 

 the acetabulum, for the articulation of the thigh bone. In only two 

 groups of reptiles, the Crocodilia and Plesiosauria, is the pubis ex- 

 cluded from union with the ilium. In the snakes and snake-like 

 lizards there are at most only vestiges of the pelvic bones. 



The pelvis of the terrestrial temnospondylous amphibians (Fig. 



1 14 a) is almost indistinguishable from that of the contemporary 



