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life, in its higher forms. 
the top with single fangs, called False Molars; and three 
behind all with compound fangs, and broad, somewhat 
hollow surfaces, called True Molars or grinders. In those 
races which feed exclusively on flesh, the molar teeth par- 
take of a cutting character, while in those that subsist on 
gram and herbage, the molar or grinding structure pre- 
vails throughout the whole. Sometimes the incisors are 
curiously developed: in the Squirrel, Eat, and similar 
animals (Rodentia), they project forwards in a curve, 
meeting at an angle, and are continually growing; in the 
Elephant, they stand out in the form of huge curved 
tusks ; and m the Narwhal, one is commonly undeveloped 
while the other grows into a long spirally-twisted straight 
tusk, like a horn, in front of its head. The Whale has°no 
teeth, but a series of horny plates, parallel to each other, 
depends from the upper jaw, and constitutes the valuable 
substance called whalebone. In the Ant-eaters, and some 
others of the Edentata, there are no teeth at all, while 
the Armadillo has ninety-six, and some of the Dolphins 
have a hundred and fifty. 
Considerable variation, suggesting diversity in function 
and habit, is also found in the forms assumed by the ex- 
tremities. The Carnivorous tribes, the Rodents, and some 
others, are furnished with paws, divided into toes, which 
are terminated by claws; and thus their feet are not only 
supports in walking, but are endowed with a grasping, tear- 
ing, or scraping power. On the other hand, the feet°of the 
Thick-skinned and Ruminant tribes are encased in solid 
hoofs of horn, which may be single, as in the Horse; 
double, as in the Sheep ; three, as in the Rhinoceros; four' 
as in the Hog; or five, as in the Elephant. A hoofed 
