VERTEBRATA. 



321 



Fig. 299.— a, Head of a Harmless Snake (upper view); b, heads of various Venomous 



Snakes. 



pil is round, and the tail tapering. This rule, however, 

 has many exceptions. 



2. Lacertilia, or Lizards, may be likened to Snakes pro- 

 vided with four limbs, each having five digits. 165 The 

 body is covered with horny scales. All have teeth, which 

 are simple in structure; and the halves of the lower jaw 

 are firmly united in front, w T hile those of Snakes are 



