330 



THE HUMAN BODY. 



embraced by the edge of the gum, is a narrowed portion, the 

 neck or cervix. From differences in their forms and uses 

 the teeth are divided into incisors, canines., bicuspids and 

 molars, arranged in a definite order in each jaw. Beginning 

 at the middle line we meet in each half of each jaw with, 

 successively, two incisors, one canine, and two molars in the 

 milk set; making twenty altogether in the two jaws. The 

 teeth of the permanent set are thirty-two in number, eight in 

 each half of each jaw, viz. beginning at the middle line- 

 two incisors, one canine, two bicuspids, and three molars. 

 The bicuspids, or premolars, of the permanent set replace the 

 milk molars, while the permanent molars are new teeth added 

 on as the jaw grows, and not substituting any of the milk- 

 teeth. The hindmost permanent molars are often called the 

 wisdom-teeth. 



Characters of Individual Teeth. The incisors (Fig. 106) 

 are adapted for cutting the food. Their crowns are chisel- 

 shaped and have sharp horizontal cutting edges, which be- 

 come worn away by use so that they are bevelled off behind 

 in the upper row, and in the opposite direction in the lower. 

 Each has a single long fang. The canines (Fig. 107) are 

 somewhat larger than the incisors. Their crowns are thick 

 and somewhat conical, having a central point or cusp on the 

 cutting edge. In dogs, cats and other carnivora the canines 

 are very large and adapted for seizing and holding prey. 

 The bicuspids or premolars (Fig. 108) are rather shorter than 



FIG. 106. 



FIG. 1 



FIG. 108. 



FIG. 109. 



FIG. 106. An incisor tooth. 



FIG. 107. A canine or eye tooth. 



FIG. 108. A bicuspid tooth seen from its outer side; the inner cusp is, accord- 



ingly, not visible. 



FIG. 109. A molar tooth. 



i*E. 



the canines and their crowns are somewhat cuboidal^Each 

 has two cusps, an outer towards the cheek, and an inner on 

 the side turned towards the interior of the mouth. The fang 



