502 ZOOLOGY. 



the fact that the pigment cells or chrornatophores are under 

 the influence of the voluntary nerves. 



While the scales of the body are developed, as a rule, from 

 the epidermis, in the scink there are dermal scales (scutes), 

 and such dermal plates in the head may unite Avith the bones 

 of the skull. In most lizards, all except the Geckos, the 

 vertebra? are procoelous, i.e., with a ball-and-socket joint, 

 the vertebrae being rounded in front, and concave behind. 

 In the Geckos the vertebral column is fish-like, the notochord 

 persisting except in the centre of each vertebra, which is bi- 

 concave. In many lizards (Lacerta, Iguana and the Geckos), 

 the middle of each caudal vertebra has a thin cartilaginous 

 partition, and it is at this point that the tails of these liz- 

 ards break off so easily when seized. In such cases the tail 

 is renewed, but is more stumpy. The tail of the specimen 

 of Sceloporus (Fig. 440) which we dissected is much shorter 

 than in the normal animal, and must have grown out after 

 having been lost. 



The throat is often distensible by the hyoid apparatus ; 

 but the bones of the jaws are firm, the bones united in front. 

 Both jaws are provided with teeth, while some have them, 

 developed on the palatine and pterygoid bones. The teeth 

 are usually simple, sharp, conical, as in most lizards, includ- 

 ing the Monitor, or they are flattened, blade-like, with ser- 

 rated edges, as in the Iguana, or as in Cydodus they are- 

 broad, adapted for crushing the food. Most lizards prey on 

 insects ; some live on plants. New teeth are usually devel- 

 oped at the bases of the old ones. They are attached to the 

 surface of its jaws; in certain extinct forms (Thecodonfs) 

 they are lodged in sockets. (Huxley.) The eyelids are 

 well developed except in the Geckos, in which the lids are 

 modified somewhat, as in the snakes, to form a transparent 

 skin over the cornea of the eyes. The tongue is free and 

 long, sometimes forked ; in the iguana it ends in a horny 

 point. 



While the limbs are usually present, one or the other pair 

 may in rare cases (in Pscudopus the fore feet are wanting ; in. 

 Chirotes the hind feet are absent) be absent, or as in Am- 

 phisbcena and its allies the feet are entirely Avanting, though 



