128 MAMMALIAN DENTITION 



medially than the molars. The first lower premolar in the speci- 

 men figured shows a definite sectorial form, much more pro- 

 nounced than in some other species. Of the molars the second 

 is the largest and the third is very variable in size. The uppers 

 exhibit the typical trigon, an oblique ridge connecting proto- 

 cone with metacone, and a hypocone the development of 

 which differs according to the species. In all the lower molars 



Fig. 45.— Dentition of Gibbon (Hylobates hoolock? Harlan; 9.88-1). The Gibbon 

 is a form less specialized than the larger Anthropoids. This example is a young male 

 with the third molar not yet erupted. 



in the figure there is a pronounced hypoconulid almost 

 axial in position and in no species is a paraconid present. The 

 hypoconid is large and by its approximation to the metaconid 

 shuts off the protoconid from the entoconid as in Propliopith- 

 ecus. 



The Gibbon then is an Anthropoid which, so far as we 

 know, never attained large proportions but, diverging from 

 the ancestral stock, specialized in its elongating muzzle and 

 tooth forms toward a frugivorous adaptation. 



