THE SKIN AND SKELETON. 
135 
is represented by a great variety of appendages to the 
skin, which are mainly organs for protection, not for sup¬ 
port. Some are horny 
developments of the ep¬ 
idermis, such as hairs, 
feathers, nails, claws, 
hoofs, horns, and the 
scales of Reptiles; oth¬ 
ers arise from the hard¬ 
ening of the dermis by 
calcareous matter, as the 
! x* T 7 * i ,\ i Fig. 101.— Skeletal Architecture in the Armadil- 
scales OT t ishes, the bony lQj showiug the relation of the carapax to the 
plates of Crocodiles and vertebral column. 
Turtles, and the shield of the Armadillo. 
The scales of Fishes (and likewise the spines of their 
vertical fins) lie imbedded in the overlapping folds of the 
skin, and are covered with a thin, slimy epidermis. The 
scales of the bony Fishes (Perch, Salmon, etc.) consist of 
Fig. 102_Diagrammatic Section of the Skin of a Fish (Carp ): a, derm, showing lam¬ 
inated structure with vertical fibres, hi c, gristly layer; e , laminated layer, with 
calcareous granules; d , superficial portion developing into scales ; /, scale-pit. 
two layers, slightly calcareous, and marked by concentric 
and radiating lines. Those of the Shark have the structure 
of teeth, while the scutes, or plates, of the Crocodiles, 
Turtles, and Armadillos are of true bone. 
The scales of Snakes and Lizards are horny epidermal, 
plates covering the overlapping folds of the true skin. 
In some Turtles these plates are of great size, and are 
called “ tortoise-shell;” they cover the scutes. The scales 
on the legs of Birds, and on the tail of the Beaver and 
Rat, have the same structure. Nails are flattened horny 
plates developed from the upper surface of the fingers 
