VERTEBRATA. 



321 



FiQ. 299 — -a. Head of a Harmless Snake (upper view) ; 6, heads of varioii? 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."" Tiie 

 bod}' 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, while those of Snakes are 





Fio. 300.— Lizard (Lacerta). 



21 



