208 



REPTILIA. 



vertebrae in all living Crocodilia are proccelous, or concave in 

 front, but in the extinct forms they may be either amphicoel- 

 ous (concave at both ends) or opisthocoelous (concave behind). 

 The vertebral ends of the anterior trunk-ribs are bifurcate. 

 There are two sacral vertebrse. The cervical vertebrae have 

 small ribs ; and there are generally false abdominal ribs pro- 

 duced by the ossification of the tendinous intersections of the 

 recti muscles. There are no clavicles. The heart consists of 

 four completely distinct and separate cavities. All the four 

 linibs are present, the anterior ones being pcntadactylous, the 

 'posterior tetradactylous. All are oviparous. 



The chief points by which the Crocodiles are distinguished 

 from their near allies the Lacertilians, are the possession of a 

 partial bony dermal exoskeleton in addition to the ordinary 

 epidermic covering of scales, the lodgment of the teeth in 

 distinct sockets, and the fact that the mixture of venous and 



Fig. 55S. — A, Head and anterior portion of tlie body of Crocodibis pondicericums ; 

 B, Hind-foot of the same. (After Gnntlier. ) 



arterial blood, which is so characteristic of Eeptiles, takes 

 place, not in the lieart itself, but in its immediate neiglibour- 

 hood, by a communication between the pulmonary artery and 

 aorta directly after their origin. 



