HOW -ANIMALS EAT. 67 
more complete set, but Saurians possess the most perfect 
dentition. The number is not fixed even in the same 
species: in the Alligator it varies from 72 to 88. The 
teeth are limited to the jawbones in the higher forms 
(Saurians); but in others, as the Serpents, they are planted 
also in the roof of the mouth. With few exceptions, they 
are conical and curved (Fig. 35). In the Serpents they 
are longest and sharpest; and the venomous species have 
two or more fangs in the upper jaw. These fangs contain 
n g m 
a canal, through which the 
poison is forced by muscles 
which compress the gland. 
The bones to which they 
are attached are movable, = 
and the fangs ordinarily lie i 
flat upon the guns, but are Fie. 31.—Poison Apparatus of the Rattle- 
oral te a ‘ snake: g, gland, with duct, leading to 
brought into a vertical POS1- the fang, f; m, elevator muscles of the 
tion in the act of striking. s¥.simch i conmacting, compres te 
As a rule, the teeth of Rep- ‘eJawss ™ nostril. 
tiles are simply soldered to the bone which supports them, 
or lodged in a groove; but those of Crocodiles are set in 
sockets. Reptilian teeth are made of dentine and a thin 
layer of cement, to which is added in most Saurians a 
coat of enamel on the crown. 
In the majority of Mammals, the teeth are limited in 
number and definite in their forms. The number ranges 
from 1 in the Narwhal (but the longest tooth in the king- 
dom) to 220 in the Dolphin. The average is 32, occurring 
in Ruminants, Apes, and Man; but 44 (as in the Hog and 
Mole) is called the typical or normal number, and this 
number is exceeded only in the lowest groups. When 
more than 44, the teeth are of the Reptilian type, small, 
pointed, and of nearly equal size, as in the Porpoise. In 
the higher Mammals, the teeth are comparatively few, 
and differ so much in size, shape, and use, that they can 
