502 ZOOLOGY. 
the fact that the pigment cells or chromatophores 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 with the bones. 
of the skull. In most lizards, all except the Geckos, the 
vertebrae are procelous, ¢.¢., with a ball-and-socket joint, 
the vertebree 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 Jguana, or as in Cyclodus 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 (Thecodonts) 
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 Psewdopus the fore feet are wanting ; in 
Chirotes the hind feet are absent) be absent, or as in Am- 
phisbena and its allies the feet are entirely wanting, though 
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