GENERAL CHARACTERISTICS. 13 



being formed of a double series of horny lobes in the basal half of the tail, beyond 

 which it is single. The head terminates in a flattened snout of variable length, 

 and is attached to the body by a short, although muscular neck ; while the bulky 

 body is much depressed. The toes are more or less webbed. Externally, the back, 

 tail, and under-parts of these animals are protected by an armour of quadrangular 

 horny shields of varying size, which are arranged in regular longitudinal and 

 transverse rows, and are in contact with one another by their edges. In the 

 region of the back, and sometimes also on the under surface of the body, these 

 horny shields are underlain by a corresponding series of pitted bony plates. In 

 the region of the neck, among existing members of the order, these bony plates 

 are often irregular in form, and vary in number, but on the back they are always 

 quadrangular and broader than long, with a well-marked longitudinal ridge down 

 the middle. Such plates form a considerable number of longitudinal rows ; each 

 plate articulating by its edges with those on either side, while those of each 

 transverse row overlap those immediately behind them. When a bony shield is 

 developed on the under surface of the body, the number of longitudinal rows of 

 plates in existing forms is always more than eight ; the transverse rows of plates 

 overlapping and each plate being composed of two distinct pieces united together 

 by suture. The limbs are provided with five toes in front and four behind ; the 

 three innermost digits in each foot being furnished with claws. In all crocodiles, 

 whether living or extinct, the conical teeth, which may be of very large size, are 

 confined to the margins of the jaws, where they are implanted in distinct sockets ; 

 while those in use are continually being replaced by fresh ones growing from 

 beneath. These animals are further characterised by their nostrils opening at the 

 extremity of the snout — which may be either short or long — and by their ears being 

 covered with movable lids. 



Such are some of the leading external features of these reptiles, and although 

 they would suffice to distinguish them from the living members of the order, 

 they are insufficient to determine their true affinities. Laying stress upon the 

 above-mentioned characters of their teeth, the naturalist is accordingly compelled 

 to resort to the skeleton and soft internal parts for more distinctive characters. 

 In the skull all crocodiles are characterised by the quadrate-bone (of which the 

 position is indicated in the figure on p. 2) being firmly united with the adjoining 

 bones ; while a further distinctive feature is to be found in the presence of two 

 bony bars on the sides of 

 the skull behind the socket 

 for the eye, the uppermost 

 of these arches being shown 

 immediately below the ^ ^v^^— --£r^±faM^^^ 



letter T in the accompany- sn)E VIEW 0F gK . ULL 0P EXTINCT CROC odile (Peiagosaurus). 



ing figure, while the lower 0> socket for the eye ; T, temporal pit or fossa. 



and more slender one forms 



the backward continuation of the inferior margin of the eye-socket. The more 

 anterior ribs (which, as in other Reptiles, are present in the neck as well as in the 

 chest) generally articulate with the backbone by means of two distinct heads; 

 and, while collar-bones are wanting, there is a breast-bone and likewise an inter- 



