134 MAMMALIAN DENTITION 



open laterally. Inturning of the hinder ends of the dental 

 arches is seen only in some individuals. 



The sloping upper and almost vertical lower incisors meet 

 edge to edge and the upper lateral tends to be pointed. The 

 canines, apart from the sexual difference, are long, except in 

 some Gibbons and are laterally directed. The upper pre- 

 molars, bicuspid in appearance, are usually set rather within 

 the line of the other cheek teeth; the first lower is sectorial 

 especially in some Gibbons and in the Orang ; the second lower 

 is large and molariform, in the Orang more than in other Anthro- 

 poids. Premolars and molars alike show crenations which 

 are so marked in the Orang as to obscure the cusp patterns; 

 they are not found in the Gibbons or Gorilla. The molars ex- 

 hibit many individual variations but in general the following 

 are characteristic. In the Gorilla the cusps are high and tri- 

 angular, in the Chimpanzee nipple-shaped, in the Orang flat and 

 little marked, in the Gibbon high and rounded. The crowns 

 are rhomboidal above, elongated below except in the Gib- 

 bons, and form areas of contact of considerable extent be- 

 tAveen the successive teeth. In the upper molars the hypocone 

 is very Avell marked except in the Orang and the oblique ridge 

 is distinct. These features may not be seen so clearly in the 

 third molar which varies greatly in size. In both second and 

 third molars there is a tendency toward reduction of the 

 metacone and hypocone. The second molar is usually the 

 largest. In the lower molars there is sometimes a vestige of the 

 paraconid shear in the Gorilla alone. In the dentition of this 

 animal the metaconid lies a little more posterior to the proto- 

 coled than in other Anthropoids. The distance between the 

 metaconid and the entoconid is considerable and a deep cleft 

 occurs on the lateral border of the crown between protoconicl 

 and hypoconid. The last-mentioned cusp varies considerably in 

 size but may be quite small and in any case does not project 

 laterally beyond the protoconid. Its base adjoins that of the 

 large metaconid and this connection separates the tAvo other 

 principal cusps. The groove which reaches the inner border 



