THE TEETH 



417 



The last tooth in the lower jaw is a true molar (Fig. 335) ; it has 

 no predecessor in the milk dentition. From its peculiar shape, and 

 because it shears against the upper sectorial or third premolar, it is 

 called the lower sectorial. In form, it resembles a reversed upper 

 sectorial, turned with its posterior end in front, its anterior end, lacking 

 the two small cusps, behind, and the inner surface outward. 



The cutting blade of the crown is formed of two nearly equal 

 cusps, the paraconid and the protoconid, which meet in a wide angle. 

 They are separated on the convex outer surface by a vertical fissure, 

 and on the concave inner surface by a deep pit. The anterior and 

 posterior edges of the blade are almost vertical. 



The greater part of the crown is supported by the large anterior 

 fang, which is curved and laterally compressed ; its tip is truncated 

 and its small posterior surface deeply grooved. The small posterior 

 fang is straight and supports only the back of the tooth. 



The lower sectorial is placed slightly obliquely in the lower jaw ; 



FIG. 337. 



RELATIONS OF UPPER AND LOWER TEETH. INNER ASPECT, 

 a, anterior cusp ; 6, middle cusp ; c, posterior cusp ; d, talon ; e, inner cusp. 



the posterior end is near the outer edge of the alveolar border, and 

 the anterior end passes to the inner side of the posterior end of the 

 second premolar. The greater part of the outer surface wears against 

 the inner surface of the cutting blade and of the internal cusp of the 

 upper sectorial ; a small posterior external part is concave and is cut 

 by the anterior edge of the small upper molar (Fig. 337). 



AVhen the jaws are closed and at rest, the only teeth in contact are 

 the incisors and the canines. The lower incisors, normally, strike 

 behind the upper incisors in such manner that the crowns of the two 



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