REPTILES. 



30I 



Fig. 297. 

 Wiedersheim, 

 z7, ilium ; is, ischium ; 

 piepubic process. 



Pelvis of Haiteria, after 



fo, obturator foramen ; 



, pubis; pr. 



Others, except theromorphs, they are represented by processes 

 upon the coracoids. The scapula, except in chelonia, is ex- 

 panded dorsally, while the coracoids are flattened, and either 

 meet in the middle line as in 

 the ichthyosaurs and plesiosaurs, 

 or they may connect with the 

 sternum. A clavicle is usually 

 present ; in the turtles it may 

 enter into the composition of the 

 plastron (Fig. 305). An epi- 

 coracoid occurs in some lizards 

 ,and turtles. 



A pelvis is more constant in 

 appearance than is the shoulder 

 girdle, vestiges of it (ischia) appearing in certain snakes. It is 

 characterized by the great development of the ilium and by 

 marked variations in the pubic bone, which in all except croco- 

 diles and pterodactyls participates in the formation of the ace- 

 tabulum. In many dinosaurs the pubis is differentiated into 

 pre- and postpubic portions (Fig. 298) ; and traces of the pre- 

 pubis may be recognized in many other groups, and also in 

 birds, as anteriorly directed processes arising from the pubis. 



The fore and hind limbs are 

 much alike in their general struc- 

 ture, and distinctively reptilian 

 features are most marked in the 

 distal portions. In the lower rep- 

 tiles, as in chelonians, the carpal 

 bones are much as in amphibia; 

 but elsewhere there is a tendency 

 to fusion, intermedium and cen- 

 trales uniting with the radiale, 

 while the carpales are similarly 

 reduced in number by fusion. In 

 the hind limbs much the same 

 features can be seen, except that the tarsal bones can fuse to 

 an even greater extent. In both carpus and tarsus there is a 

 tendency for the proximal row to become closely united to the 



Fig. 298. Pelvis of Iguanodon, 

 after Dollo. a, acetabulum ; il, 

 ilium ; is, ischium ; po, postpubis ; 

 pr, prepubis. 



