134 COMPARATIVF, ZOOLOGY. 
The scales of 
Snakes and Lizards 
are horny epiderm- 
ic plates covering 
the overlapping 
folds of the true 
skin. In some Tur- 
tles these plates are 
of great size, and 
are called “ tor- 
toise-shell;” they 
cover the bony 
Fs r 
Fic. 103,—Vertical Section of the Forefoot of the Horse dermal plates. The 
(middle digit): 1, 2,4, proximal, middle, and distal, 
or ungual, phalanges; 3, sesamoid, or nut-bone; 5, 
scales on the legs 
6, 7, tendons; 9, elastic tissue; 8/10, internal and of Birds and on 
external floor of the hoof; 11, 12, internal and ex- ’ 
ternal walls. 
Beaver and Rat, have the same 
structure. Nails are flattened 
horny plates developed from the 
upper surface of the fingers and 
toes. Claws are sharp conical 
nails, being developed from the 
sides as well as upper surface ; 
and hoofs are blunt cylindrical 
claws. Hollow horns, as of the 
Ox, may be likened to claws 
sheathing a bony case. The horn 
of the Rhinoceros is a solid mass 
of epidermal fibres. “ Whale- 
bone,” the rattles of the Rattle- 
snake, and the beaks of Turtles 
and Birds, are likewise epidermal. 
Hairs, the characteristic clothing 
of Mammals, are elongated horny 
cones, composed of “pith” and 
the. tails o£) the 
wy 
Fra. 104.—Section of the Root and 
part of the Shaft of a Human 
Hair; it is covered with epi- 
dermic scales, the inner layer, 
ec, forming the outer covering 
of the shaft, being imbricated ; 
the root consists of angular 
cells loaded with pigment. 
