TEETH DIVISIONS. 63 



termination of the nasal duct, and the opening of the naso-palatine 

 canal. The nasal fossce commence upon the face by a large irregu- 

 lar opening, the anterior nares, and terminate posteriorly in the 

 two posterior nares. 



TEETH. 



Man is provided with two successions of teeth ; the first are the 

 teeth of childhood, they are called temporary or deciduous ; the 

 second continue until old age, and are named permanent. 



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

 jaw; they are divisible into four classes, incisors, of which there 

 are four in each jaw, two central and two lateral; canine, two 

 above and two below ; bicuspid, four above and four below ; and 

 molars, six above and six below. 



The temporary teeth are twenty in number ; eight incisors, four 

 canine, and eight molars. The temporary molars have four 

 tubercles, and are succeeded by the permanent bicuspides, which 

 have only two tubercles. 



Each tooth is divisible into a crown, which is the part apparent 

 above the gum; a constricted portion around the base of the 

 crown, the neck ; and a root or fang, which is contained within the 

 alveolus. The root is .invested by periosteum, which lines the 

 alveolus, and is then reflected upon the root of the tooth as far as 

 its neck. 



The incisor teeth (cutting teeth) are named from presenting a 

 sharp and cutting edge, formed at the expense of the posterior sur- 

 face. The crown is flattened from before backwards, being some- 

 what convex in front and concave behind ; the neck is considerably 

 constricted, and the root compressed from side to side ; at its apex 

 is a small opening for the passage of the nerve and artery of the 

 tooth. 



The canine teeth (cuspidati) follow the incisors in order from 

 before backwards ; two are situated in the upper jaw, one on each 

 side, and two in the lower. The crown is larger than that of the 

 incisors, convex before, and concave behind, and tapering to a 

 blunted point. The root is longer than that of all the other teeth, 

 compressed at each side, and marked by a slight groove. 



The bicuspid teeth (small molars), two on each side in each jaw, 

 follow the canine, and are intermediate in size between them and 

 the molars. The crown is compressed from before backwards, 

 and surmounted by two tubercles, one internal, the other external; 

 the neck is oval ; the root compressed, and marked on each side 

 by a deep groove, and bifid near its apex. The teeth of the upper 

 jaw have a greater tendency to the division of their roots than 

 those of the lower, and the posterior than the anterior pair. 



The molar teeth (grinders,) three on each side in each jaw, are 

 the largest of the permanent set. The crown is quadrilateral, and 

 surmounted by four tubercles, the neck large and round, and the 



