140 CROCODILES AND ALLIGATORS. 



l^itted scutes forming the shield on the back are ridged, 

 and arranged in from four to eight longitudinal rows. 

 Moreover, in the caimans and the extinct Biplocynodon, the 

 shield on the under surface of the body forms a single 

 mass, made up of more than eight longitudinal rows of 

 scutes, each of which, as already mentioned, consists of 

 two separate pieces united together by suture. 



If we now contrast these features with those obtaining in 

 the Jurassic crocodilians, we shall find very considerable 

 differences. Thus in the skull of those reptiles the fourth 

 pair of bones on the palate did not meet in the middle line 

 below the passage to the nostrils, so that the internal nos- 

 trils were placed immediately behind, or sometimes partly 

 between, the bones lying between PP in Pig. 45, and were 

 thus much forwarder than in modern crocodilians. Then, 

 again, the vertebrae were slightly cupped at both ends, thus 

 admitting of much less motion between one another. The 

 armour on the back of the body is of a similar type, consist, 

 ing only of two longitudinal rows of scutes, which lack the 

 longitudinal ridges so characteristic of those of the existing 

 forms. On the other hand, the armour on the under surface 

 was nearly always present and more developed, frequently 

 consisting of two distinct portions, in the foremost of which 

 the scutes (which consisted of a single piece) overlapped 

 like slates, while in the hinder jiart they were joined by 

 their edges to form a solid pavement of bone. 



Like their modern cousins, the Secondary crocodilians 

 included both long-snouted (Fig. 46) and short-snouted 



!FiG. 46. — Side Tiew of the Skull of an Extinct Crocodilian of the 

 Lias ; one-fourth, natural size. Letters as in Fig. 45. 



types, the former being the more common and especially 

 abundant in the lias, where their remains occur in com- 

 pany with those of fish-lizards and plesiosaurs. In many 



