316 ZOOLOGY SECT. 



-Chamseleons both fore- and hind-limbs become prehensile by a 

 special modification in the arrangement and mode of articulation 

 of the digits. In these remarkable arboreal Keptiles the three 

 innermost digits of the manus are joined together throughout their 

 length by a web of skin, and the two outer digits are similarly 

 united : the two sets of digits are so articulated that they can be 

 brought against one another with a grasping movement much 

 analogous to the grasping movements of a Parrot's foot or of the 

 hand of Man. A similar arrangement prevails in the pes, the only 

 difference being that the two innermost and three outermost digits 

 are united. In some groups of Lacertilia, on the other hand, 

 such as the Blind- Worms (Anguis), limbs are entirely absent, or 

 .are represented only by mere vestiges ; and numerous intermediate 

 gradations exist between these and forms, such as Lacerta, with 



FIG. 922. Pygopus lepidopus. (After Brehm.) 



well-developed limbs. The limbless Lizards (Fig. 922) bear a very 

 close resemblance to the Snakes, not only in the absence of the 

 limbs, but also in the general form of the body and the mode 

 of locomotion. 



The body of a Snake is elongated, narrow and cylindrical, 

 usually tapering towards the posterior end, sometimes with, more 

 usually without, a constriction behind the head. In the absence 

 of limbs the beginning of the short caudal region is only indicated 

 by the position of the cloacal opening. The fore-limbs are never 

 represented even by vestiges ; in some Pythons there are in- 

 conspicuous 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 conspicuous, points of distinction are the absence of 

 movable eyelids in the Snake, and also the absence of a tympanum. 



