186 ANTHROPOID APES. 



crown in a posterior cusp. The pre-molars have an 

 external and an inner cusp ; the roohxrs have two 

 external and two inner cusps, connected with each 

 other by their enamel. The lower canine teeth of 

 these animals are likewise of the shape of a three- 

 sided pyramid, of which the anterior angle is very 

 blunt, while the inner and posterior angles are 

 sharply cut. The anterior surface is not grooved 

 like the upper canine teeth. The lateral angle is 

 much rounded. The back teeth plainly display 

 the posterior fifth cusp, which may also be observed 

 in man. In the orang-utan the characteristics of 

 the upper incisors are such as we have described in 

 the case of other anthropoids. The upper canine 

 teeth are shaped like a three-sided pyramid, and 

 are furnished with a longitudinal furrow on the 

 anterior side. A similar furrow is found on the pos- 

 terior superficies of the lower canine teeth. The 

 back teeth display no special characteristics when 

 compared with those of other anthropoids. 



The canine teeth of these anthropoids are much 

 worn down by age on their posterior surface. Deep 

 transverse grooves of varying size characterize the 

 teeth of anthropoids, owing to the unequal distribu- 

 tion of the coating of enamel. These are developed 

 with their advancing growth. In addition to these 

 incised furrows, longitudinal marks, with raised 

 edges, also appear, and especially on the anterior 

 surface of the incisor teeth. 



In the gibbon the anterior surface of the incisor 

 teeth is smooth ; in this animal the upper central 

 incisor teeth are the largest, while the lower central 



