176 COMPAEATIVE DENTAL ANATOMY 



The others are lobed and have a small internal 

 cusp. The fourth is like the true molars, which 

 are made quadrangular by the internal cingulum 

 rising up into a cusp at the posterior angle of the 

 crown. In some forms, as the Spectre-lemur, the 

 teeth are of insectivorous type for the peculiar 

 diet. There is often a basal ridge on the incisor, 

 which is well denned even on the anterior face. 

 The inner cingule on the incisors is like those of 

 Moles. The molar series are inclined to be tri- 

 hedral. The Galeopithecus is remarkable for 

 having the lower incisors, which are broad and 

 flat, cleft to the base by deep vertical fissures, so 

 that they resemble the teeth of a comb and are 

 used in dressing the coat of the animal. There 

 are seven such fissures, making eight columns in 

 the central and nine in the lateral incisors. The 

 upper centrals are broad, flat, and notched, as are 

 also the third incisors and canines. The molar 

 series are simple and tuberculate. The Aye-Aye 

 (Cheiromys) has a dentition of the rodent type, 

 with similar continuously-growing, scalpriform 

 incisors. The lateral incisors, canines, and most 

 of the premolars are absent, the molars having 

 an elliptical grinding surface. Other forms of 

 Lemurs present different varieties of dentition. 

 They are survivors of that primitive type of 

 Quadrumana which were the progenitors of the 

 Anthropomorpha of today, — including man, — ■ 



