136 
COMPARATIVE ZOOLOGY. 
Fig. 103.—Vertical Section of the Forefoot of the Horse 
(middle digit): 1, 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. 
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 
rattles of the Rattlesnake, and the 
beaks of Turtles and Birds, are like¬ 
wise epidermal. 
Hairs, the characteristic clothing 
of Mammals, are elongated horny 
cones, composed of “pith” 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 aw r ay. The root is bulbous, 
and is contained in a minute de¬ 
pression, or sac, formed by an in¬ 
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 
Fig. 104.—Section of theRootaud 
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, beingiimbricated; 
the root consists of angular 
cells loaded with pigment. 
