222 THE ANATOMY OF VERTEBRATED ANIMALS. 



b. The nasals are excluded from the external nasal aperture. The head 

 very long; the teeth subequal. Both the first and the fourth 

 mandibular teeth bite into grooves in the margin of the upper ja«-. 

 The premaxillo-maxillary suture acutely angulated backward. The 

 mandibular symphysis extends to at least the fourteenth tooth, and 

 the splenials enter into it. The cervical and tergal scutes foiTu a 

 continuous series. 



3. Oavialidce. 



Rhynchosuchus. Gavialis. 

 B. With the- presacral vertebrae amphiccelons (the anterior vertebra! 

 sometimes opisthoccelous (?) ) ; and the posterior nares bounded by 

 the palatines, the pterygoids not being united below. (All these 

 Crocodiles are extinct and pre-cretaceous.) 



a. With the external nares terminal. 



4. 7'eleosauridce. 



Tcleosaurus, Go7iiopholis. 



Streptospondylus. Stagonolepis. Galesaurus (?). 



b. With the external nares on the upper part of the base of the snout 



near the orbits. 



6. Belodontid(e. 

 Belodon. 



There is a large number of extinct Heptilia which resemble 

 the Crocodilla in the characters of their pre-sacral vertebrsB, 

 but differ from them, and resemble JLacertilia (Jhelonia, or 

 Birds, in other respects. 



These are the Dicynodontia, the Ornithoscelida, and the 

 Pterosauria. 



VII. The DiCTisroDONTiA. — Dicynodon and Oudenodon 

 are lacertiform animals, sometimes of large size, with crocodil- 

 ian vertebrae, four or five of which are anchjlosed together to 

 form a strong sacrum. The skull is massive and lacertilian in 

 most of its characters ; but the jaws are like those of the 

 Chelonia, and were doubtless cased in a horny beak. Never- 

 theless, most of the species possess two great tusks, which 

 grow from persistent pulps, lodged in a deep alveolus of either 

 maxilla. The limbs appear to have been subequal and massive, 

 with short and stout feet. The scapula and coracoid are 

 simple and expanded, and there seems to have been no clav- 

 icle. The pelvis is very strong, with widely-expanded ilia, 

 ischia, and pubes. The two latter meet in a median ventral 

 symphysis, and the pubis and ischium of each side meet and 

 obliterate the obturator foramen. The limb-bones are lacer- 

 tihan in character. 



Remains of these Reptiles have hitherto been found only 

 in strata, which probably belong to the Triassic formation, in 

 India and South Africa, and the Ural Mountains. 



