TEETH OF DIPHYODONTS. 317 



and strong slightly-curved crown, extending below the alveolar 

 border of the under jaw when the mouth is shut, with a 

 moderately sharp posterior margin, but without an anterior 

 groove. In the female Orang the canines are smaller ; the crowns 

 extend only a short distance beyond the level of the adjoining 

 molars. In the upper jaw both premolars and molars are im- 

 planted by three diverging roots, two external and one internal ; 

 in the lower jaw the corresponding teeth have two strong di- 

 verging roots ; the series of grinders forms a straight line on each 

 side of both jaws. 



As the precise characteristics and ordinal distinction of the 

 human dentition are best demonstrated by comparison with that 

 brute species which is most nearly allied to man, the details of 

 such a comparison will here be given and illustrated more fully, 

 as manifested in the Gorilla ( Troglodytes Gorilla). Fig. 253 

 gives a side view of the teeth of a male full-grown, but not aged, 



O O -* O - 7 



specimen of this species. In the upper jaw the middle incisors 

 are smaller, the lateral ones i, 2, larger than those of the Orang ; 

 they are thus more nearly equal to each other ; nevertheless the 

 proportional superiority of the middle pair is much greater than 

 in Man, and the proportional size of the four incisors both to 

 the entire skull and to the other teeth is greater. Each incisor 

 has a prominent posterior basal ridge, and the outer angle of the 

 lateral incisors i, 2, is rounded off as in the Orang. The incisors 

 incline forward from the vertical line as much as in the Orano*. 



e> 



Thus the characteristics of the human incisors are, in addition to 

 their true incisive wedge-like form, their near equality of size, 

 their vertical or nearly vertical position, and small relative size 

 to the other teeth and to the entire skull. The diastema between 

 the incisors and the canine on each side is as well marked in the 

 male Gorilla as in the male Orang. The crow r n of the canine, 

 fig. 253, c, passing outside the interspace between the lower 

 canine and premolar, p 3, extends in the male Troglodytes Gorilla 

 a little below the alveolar border of the under jaw when the 

 mouth is shut ; the upper canine of the male Troglodytes niger 

 likewise projects a little below that border. In the male of the 

 Chimpanzee ( Troglodytes niger\ the upper canine is conical, 

 pointed, but more compressed than in the Orang, and with a 

 sharper posterior edge ; convex anteriorly, becoming flatter at 

 the posterior half of the outer surface, and concave on the cor- 

 responding part of the inner surface, which is traversed by a 

 shallow longitudinal impression ; a feeble longitudinal rising and 

 a second linear impression divide this from the convex anterior 



