310 THE HUMAN BODY. 



two semicircles, formed by the borders of the upper and 

 lower jaw-bones, which are covered by the gums, except at 

 intervals along their edges where they contain sockets in 

 which the teeth are implanted. During life two sets of 

 teeth are developed; the first or milk set appears soon after 

 birth and is shed during childhood, when the second 

 or permanent set appears. 



The teeth differ in minor points from one another, but 

 in all three parts are distinguishable; one, seen in the 

 mouth and called the crown of the tooth; a second, im- 

 bedded in the jaw-bone and called the root or fang; and 

 between the two, 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 wis- 

 dom teeth. 



Characters of Individual Teeth. The incisors (Fig. 

 90) are adapted for cutting the food. Their crowns are 

 'chisel - shaped and have sharp horizontal cutting edges, 

 which become worn away by use so that they are beveled 

 off behind in the upper row, and in the opposite direction 

 in the lower. Each has a single long fang. The canines 

 (Fig. 91) 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. 92) are rather shorter than the canines and their 



