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- 
v 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 
Fig. 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 
