V& TEETH CLASSIFICATION. 



ing of the frontal sinuses, of the anterior ethmoid cells, and of the antrum. 

 The largest of the three passages is the inferior meatus, which is the space 

 between the inferior turbinated bone and the floor of the fossa ; in it there 

 are two foramina, the termination of the nasal duct, and one opening of 

 the anterior palatine canal. The nasal fossae commence upon the face by 

 a large irregular 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, deciduous, or milk teeth ; the 

 second continue until old age, and are named permanent. 



/ g h 



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 (fig. 44) ; 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 surface. The crown 

 is flattened from before backwards, being somewhat convex in front and 

 concave behind ; the neck is considerably constricted, and the root com- 

 pressed from side to side ; at its apex is a small opening for the passage 

 of the nerve and artery of the tooth. 



* Permanent teeth, a. Central incisor, b. Lateral incisor, c. Cuspid or canine 

 d. First bicuspid, e. Second bicuspid. /. First molar, g. Second molar, h Third 

 molar or dens sapientia. 



