288 THE VERTEBRATE SKELETON. 



Chelonia, Ophidia, and most of the snake-like Amphisbaenidae 

 among Lacertilia ; while it is not well known in Theromorpha 

 and Dinosauria. In the Sauropod Brontosaurus, however, two 

 rounded bones occur near the base of the coracoids, and these 

 probably represent ossified patches in a sternum, which was 

 mainly cartilaginous ; similar structures occur in Iguanodon. 



The sternum frequently remains wholly cartilaginous, 

 especially in Lacertilia ; sometimes it becomes calcified, but 

 true ossification does not as a rule take place. 



APPENDICULAR SKELETON. 



THE PECTORAL GIRDLE. 



The pectoral girdle is well developed in all groups of 

 reptiles except the Ophidia, occurring even in the limbless 

 Amphisbaenidae. It is very solid in the Theromorpha. As a 

 rule all three cartilage bones, scapula, coracoid, and precoracoid 

 are represented, and frequently also the membrane bones, 

 clavicles, and interclavicle. 



The coracoids are generally flat expanded bones, which 

 sometimes, as in Sauropterygia and Ichthyosauria, meet in a 

 ventral symphysis ; sometimes, as in Lacertilia, are united with 

 the sides of the sternum. In Chelonia neither the coracoids 

 nor precoracoids meet one another, but their free ends are 

 connected by nbro-cartilaginous bands. In Lacertilia the 

 coracoids are pierced by fenestrae. 



The precoracoid is generally represented, but the Thero- 

 morpha are the only reptiles in which it is separately ossified; 

 it forms a well-marked process on the coracoid in Lacertilia 

 (fig. 54, 5). It is absent in Ichthyosauria, and Dinosauria, 

 and probably in Sauropterygia. In some Lacertilia and 

 Chelonia the sternal ends of the coracoids are unossified and 

 form epicoracoids ; in some Chelonia there are also epipre- 

 coracoids ; but neither these nor the epicoracoids overlap their 

 fellows of the opposite side as they do in arciferous Anura 

 (see p. 185). In some Lacertilia with degenerate limbs the 



