PHYLUM CHORD ATA 



341 



Reptile with a well-developed laterally-compressed tail, and 

 pentadactyle extremities, very similar to those of a typical Lizard. 

 The upper surface is covered with small granular scales, and a 

 crest of compressed spine-like scales runs along the middle of the 

 dorsal surface. The lower surface is covered with transverse rows 

 of large squarish plates. 



In the^Chelonia (Fig. 980) the body is short and broad, enclosed 

 in a hard " shell " consisting of a dorsal part or carapace and a 

 ventral part or plastron. These are in most cases firmly united, aper- 

 tures being left between them for the head and neck, the tail and 

 the limbs. The neck is long and mobile ; the tail short. The limbs 

 are fully developed though short. In some (land and fresh-Water 



Fig. 980.— Grecian Tortoise (Testudo grieca). (After Brehm.) 



Tortoises) they are provided each with five free digits terminating 

 in curved horny claws ; in the Turtles the digits are closely united 

 together, and the limb assumes the character of a " flipper " or 

 swimming paddle. The cloacal aperture is longitudinal. 



The Crocodilia, the largest of living Reptiles, have the trunk 

 elougated and somewhat depressed, so that its breadth is much 

 greater than its height. The snout is prolonged, the neck short, 

 the tail longer than the body and compressed laterally. The 

 hmbs are relatively short and powerful, with five digits in the 

 manus and four in the pes, those of the latter being partly or 

 completely united by webs of skin. The eyes are very small ; the 

 nostrils placed close to the end of the snout and capable of being 

 closed by a sphincter muscle. The cloacal aperture is a longi- 

 tudinal slit. The dorsal and ventral surfaces are covered with 

 thick, squarish horny scales, often sculptured or ridged, those 



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