THE ALIMENTARY APPARATUS. 219 



It is invested throughout (except on the teeth) with highly 

 vascular mucous membrane covered with stratified squamous 

 epithelium containing conical papilla?. 



It presents for examination the following parts : 



THE TEETH. The teeth are firmly implanted within the 

 alveoli of the jaws and surrounded by the gums. 



The gums are composed of dense fibrous tissue, covered by 

 smooth, vascular, mucous membrane of slight sensibility. This 

 fibrous tissue is continuous with the periosteum of the jaws, and 

 forms about the neck of the teeth a constricted ring the dental 

 ligament. 



There are four kinds of teeth incisors, canines or cuspids, 

 premolars or bicuspids, and molars. MAN is provided with two 

 sets of teeth, the temporary, deciduous, or milk teeth, which 

 appear in childhood, and the permanent, which appear after the 

 shedding of the milk teeth and last until old age. 



The temporary or deciduous teeth are twenty in number, 

 ten in each jaw, or five in each side of each jaw : 



Two incisors, one canine, and two molars. 



The permanent teeth are thirty-two in number, sixteen in 

 each jaw, or eight in each side of each jaw : 



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



Each tooth consists of three parts : 



Crown, or body, the enameled portion above the gum; neck, 

 the constricted portion between the crown and root; root, or 

 fang, within the alveolus, and covered with cement. 



Characteristics. Incisors, or cutting, are so called from 

 their wedge-shaped, chisel-like crown, being adapted for biting 

 or cutting the food. The fang is long, single, conical, and com- 

 pressed at the sides. 



Cuspids, or canines, have been so named from their con- 

 spicuous character in the canine or dog tribe. 



The crown is large, conical, convex in front, and beveled 

 behind. The fang is single, longest, and thickest of all the 

 teeth. 



Bicuspids, or premolars. The crown has a pair of project- 

 ing tubercles or cusps. Fang is conical, single, but deeply 

 grooved, indicating a disposition to bifurcate. 



Molars, commonly known as grinders or jaw teeth. Crown, 

 broad, quadrilateral, with four cusps in upper, five in lower 

 molars. Lower molars have usually a pair of fangs placed lat- 

 erally; the upper, three fangs, two external and one internal. 



The last or third molar has but one fang (with a tendency 

 to divide into the same number of roots as the other molars), and 

 is known as the dens sapientice, or " wisdom tooth," from its 

 late appearance. 



