PHYLUM CHORDATA 



437 



the absence of limbs, the beginning of the short caudal 

 region is only indicated by the position of the cloacal open- 

 ing. The fore-limbs are never represented even by vestiges ; 

 in some pythons there are inconspicuous vestiges of hind- 

 limbs, in the form of small claw-like processes. The mouth 

 of the snake is capable of being very widely opened by the 

 free articulation of the lower jaw, and it is this mainly which 

 distinguishes it from the snake-like lizards. But other, less 



Fig. 261. — Pygopus lepidopus. (After Brehm ) 



conspicuous, points of distinction are the absence of movable 

 eyelids in the snake, and also the absence of a tympanum. 



Hatteria, the New Zealand Tuatara (Fig. 262), the only 

 living representative of the Rhynchocephalia, is a lizard-like 

 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. 



