THE DECIDUOUS DENTITION 



247 



Its occlusal surface is long and as broad as the crown. The 

 metaconid and hypoconid are large and the hypoconulid axial 

 in position. The same description holds for the Gorilla in 

 which the metaconid is very large. In the Chimpanzee the oc- 

 clusal surface becomes restricted transversely and the hypo- 

 conulid migrates somewhat laterally, so that it is not unlike 

 the second lower molar of the Pfedmost mandible. In the 

 Orang the pinched-in condition of the occlusal surface is very 



Fig. 89. — Deciduous dentition of Gorilla (Gorilla sp., 9.88-12). 



pronounced though the hypoconulid remains more axially 

 situated than in man. The molars resemble quite considerably 

 the lower first milk molar of the human dentition, a case of 

 convergent evolution in which the terminal appearance has 

 been brought about in very different manner in the two cases. 

 The forms of the two upper milk molars and the lower second 

 are comparatively easily understood. AVith regard to the 

 lower first molar it seems that in the Anthropoids with tusk- 



