136 
COMPARATIVE ZOOLOGY. 
Fig. 103—Vertical Section of the Forefoot of the Horse 
(middle digit): i, 2, 4, proximal, middle, and distal, 
or ungual, phalanges; 3, sesamoid, or nut-bone; 5, 
6, 7, tendons; 9, elastic tissue; 8, 10, internal and 
external floor of the hoof; 11,12, internal and exter¬ 
nal walls. 
rattles of the Rattlesnake, and the 
beaks of Turtles and Birds, are like¬ 
wise epidermal. 
Hairs, the characteristic clothing 
of Mammals, arc elongated horny 
cones, composed of “ pith 55 and 
“crust.” The latter is an outer 
layer of minute overlapping scales, 
which are directed towards the 
point, so that rubbing a human 
hair or fibre of wool between the 
thumb and finger pushes the root- 
end away. The root is bulbous, 
and is contained in a minute de¬ 
pression, or sac, formed by an in- fig.km.—! 
folding of the skin. Hairs are usu¬ 
ally set obliquely into the skin. 
Porcupine’s quills and Hedgehog’s 
spines make an easy transition to 
and toes. Claws 
are sharp conical 
nails, being devel¬ 
oped from the sides 
as well as upper 
surface; and hoofs 
are blunt cylin¬ 
drical claws. Hol¬ 
low horns, as of the 
Ox, may be likened 
to claws sheathing 
a bony core. The 
horn of the Rhinoc¬ 
eros is a solid mass 
of epidermal fibres. 
“ Whalebone,” the 
-Section of the Root and 
part of the Shaft of a Human 
Hair; it is covered with epi¬ 
dermic scales, the inner layer, 
c, forming the outer covering 
of the shaft, being imbricated; 
the root consists of angular 
cells loaded with pigment. 
