THE PRIMATES EXCEPT MAN 123 



are parallel, even approximated at the level of the last molar. 

 The symphysial region is fairly well filled up with bony tissue. 

 The palate extends as far back as the last molar. The incisors 

 of both jaAvs are gently procumbent. There is a great increase 

 in length of the canines different in type from that found in 

 Carnivora and suggesting another role. The upper canine is 

 much longer than the lower and is peculiarly twisted so that 

 the teeth do not interlock as in the pure flesh-feeder. This 

 elongation of the canine is partly sexual and defensive but its 

 special character is indicated by the peculiar formation of the 

 first lower premolar. This tooth is sectorial in appearance 

 and, being tilted backwards, presents a covering of enamel 

 well down its anterior root. It is obvious that the upper canine, 

 shearing between the adjacent edges of this tooth and the lower 

 canine will have great piercing and cutting power very advan- 

 tageous in biting roots and fruits which possess a thick and 

 tough rind. This adaptation of the canines and the first lower 

 premolar is very common among modern Old-World Primates 

 and indeed is one of their chief specializations. The second 

 mandibular premolar inclines to a molariform appearance ; the 

 two upper premolars are simple bicuspid teeth. Certain mark- 

 edly progressive features are present in the molar series. In 

 both maxilla and mandible the first molar is the smallest and 

 though the third is the largest in the lower jaw the second is 

 somewhat bigger than the third in the maxillary series. Trans- 

 verse ridges are apparent on the molars of both jaws and the 

 cusps are rather long. In the upper molars the hypocone is a 

 large cusp connected with the metacone by a ridge.* In the 

 loAver molars the paraconid is missing and the metaconid is 

 placed well forward and connected with the protoconid by a 

 ridge. The talonid is large but presents no hypoconulid even 

 on the third molar. 



There is still further specialization in the dentition of the 

 purely herbivorous Baboon. Papio hamadryas arabicus, the 



*The oblique ridge connecting protocone with metacone is found only in the An- 

 thropoids among Old-World non-iemurine Primates. 



