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 



1 4 TT* 1 +1 1 Fig. 101.— Skeletal Architecture in the Armadil- 



SCaleS 01 r lSlieS, tne OOny l0j ghowing t h e 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 



Fiu. 102.— Diagrammatic Section of the Skin of a Fish (Carp) : a, derm, showing lam- 

 inated structure with vertical fibres, b; 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 



