322 COMPARATIVE ZOOLOGY. 



loosely tied together by ligaments. Nearly all have a 

 breast -bone, and the eyes (save in the Gecko) are fur- 

 nished with movable lids. In the common Lizards and 

 Chameleon, the tongue is extensile. The tail is usually 

 long, and in some cases each caudal vertebra has a divis- 

 ion in the middle, so that the tail, when grasped, breaks 

 off at one of these divisions. The Chameleon has a pre- 

 hensile tail. The Iguana is distinguished by a dewlap on 

 the throat and a crest on the back. Except some of the 

 Monitors of the Old "World, all the Lizards are terrestrial. 

 3. Chelonia, or Tortoises and Turtles, are of anomalous 

 structure. The skeleton is external, so as to include not 

 only all the viscera, but also the whole muscular system, 

 which is attached internally; and even the limbs are 



Fio. 301. Hawk's-bill Turtle (Eretmochelys imbricata). Tropical Atlantic. 



inside, instead of outside, the thorax. The exoskeleton 

 unites with the endoskeleton, forming the carapace, or 

 case, in which the body is enclosed. The exoskeleton con- 

 sists of horny plates, known as "tortoise-shell" (in the 

 soft Tortoises, Trionyx, this is wanting), and of dermal 



