212 THE VERTEBRATE SKELETON. 



Suborder (2). EUSUCHIA. 



The vertebrae are either biconcave or procoelous. The pre- 

 maxillae are small, and the anterior nares are united and 

 placed far forwards. The posterior nares lie far back, the 

 palatines and in living genera the pterygoids, meeting in the 

 middle line, and giving rise to a closed palate. The supra- 

 temporal fossae are surrounded by bone on all sides, and the 

 parietals, and often also the frontals are united. There are 

 no clavicles. The suborder includes the genera Crocodilus, 

 Alligator, Garialis and others living and extinct. 



Order 9. PTEROSAURIA 1 . 



These animals, called also the pterodactyles or Ornitho- 

 sauria, are a group of extinct reptiles, whose structure has 

 been greatly modified from the ordinary reptilian type for the 

 purpose of flight. 



The skin was naked and they vary greatly in size and in 

 the length of the tail. The vertebrae and limb bones are 

 pneumatic just as in birds. The presacral vertebrae are pro- 

 coelous and have their neural arches firmly united to the 

 centra. The neck is long, the caudal vertebrae are amphi- 

 coelous, and from three to five vertebrae are fused together 

 in the sacral region. The skull is large and somewhat bird- 

 like, the facial portion being much drawn out anteriorly, and 

 the sutures being obliterated. It resembles that of other 

 reptiles in having large supratemporal fossae ; large pre-orbital 

 vacuities also occur. The jaws may be toothed or toothless, 

 and the teeth, when present, are imbedded in separate sockets. 

 The premaxillae are large, and the quadrate is firmly attached 

 to the skull. The rami of the mandible are united at the 



1 See H. G. Seeley On the Organisation of the Ornithosauria, Journ. 

 Linn. Soc. (Zoology) vol. xin. p. 84. K. A. Zittel, Ueber Flugsaurier aus 

 dem lithographischen schiefer, Palaeontograph. xxix. p. 49. 



