THE PRIMATES EXCEPT MAN 109 



deep, the paraconid remains in greatly lessened size and the 

 last molar is reduced. 



Early features of the Primate stock are then a short and deep 

 mandibular body Avith vertical incisors, a moderately large 

 canine, crowded premolars, and molars showing in the mandible 

 a large talonid and a reduced paraconid and in the maxilla a 

 simple trigon with an incipient hypocone but no styles. In 

 addition the last upper molar is only slightly reduced and the 

 last lower not at all. But even this primitive stage shows some 

 deviation from the common ancestral insectivorous Mammal. 

 Both incisors and premolars are less in number and in the 

 molars the talonid is already pronounced. 



Earlier stages in the phylogenetic history of the Eocene 

 Primates are illustrated in another extinct family of the Le- 

 murs, namely the Adapidae. In these the dental formula was: 



lf, C ipf,M§. 



In the more primitive species the premolars are only slightly 

 or not at all bicuspid and the upper molars have no hypocone. 

 In more advanced forms the upper molars show the beginning 

 of style formation. 



The loss of one incisor must have occurred at the very com- 

 mencement of Primate evolution whereas the loss of premolars 

 occurred later and has been progressive. Certain other primi- 

 tive features of the Primate mandible are the divergence back- 

 ward of the limbs of the dental arch, the absence of an "ape- 

 shelf" and the lack of bony deposit on the inner side of the 

 mandibular body in the region of the anterior teeth. 



THE LEMURS 



The Lemurs, undoubtedly the lowest group of the Primates, 

 are now represented by a number of highly specialized and 

 more or less degenerate species which, however, in spite of 

 divergences characteristic of the group, illustrate the trend of 

 progress in the dentition general to the Primates. 



