CROCODILES 2369 



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 armor of quad- 

 rangular 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 exisiting 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 trans- 

 verse 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 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 characterized 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 characteristics of their teeth, the naturalist is accordingly compelled to 

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

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

 sition is indicated in the figure on p. 2358) 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 let- 

 ter T in the accompanying SIDE VIEW OF SKULL OF EXTINCT CROCODILE (Pelagosaurus). 



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



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 breastbone and likewise an interclavicle; the 

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