206 
of the large ventral or lower scales. 
once a year, the process being 
BACKBONED ANIMALS. 
The skin is moulted 
assisted by the growth of 
casting-hairs (Fig. 247) beneath the skin, that push it 
ay sp 
: es 
b FeCecac (Quy) Wheas : 
EyTESN\ \\ —=s @ 
L& \\ } LASSER cies Aan ANT yj aS) 
HS eS RR L2\ 
eel psi 
iS Xe Re WR ZN 
re st ant My = 
Ox Pa GEST ) ns Ww, 
‘ft 5) Vie 
Ss 4 WE 
(PX 1 WE 
Pern aaa NN NY il iV TPP Pron IF LES 
N ae eay int YR Mena" a 
Ree RTAAKAAN [PRR 
! 
Fic. 246,—Skeleton of a snake. s%, spinous processes of the joints; 7, ribs ; 
g, quadrate bones, joining upper and lower jaws; e, front of the lower 
jaw, where there is an elastic band in the place of bone; 4, ball end of 
joint, facing the tail; ¢, cup end of joint, facing the head. 
FIG. 247.—Casting process in the skin 
of the adder. 4 4, the casting hairs ; 
the portion of skin above them is 
pushed away, and the hairs themselves 
form the ridges on the new skin. 
upward. In the North 
they hibernate in win- 
ter, and in the South 
pass through a summer 
sleep. Over one thou- 
sand species are known, 
one hundred and thirty 
species being found in 
North America. 
The Vipers (/- 
pertde).— About twenty- 
two species of these 
snakes are known. In 
the puff-adder, of the 
Cape of Good Hope, the 
