THE LEMURS. 11 



There is an oblique ridge between the hind outer and the 

 front inner cusp, and another is often present between the 

 front outer cusp and the anterior "heel," producing, as Huxley 

 has pointed out, almost a double crescentic pattern, as in many 

 lower Mammals. The posterior molar has four or five cusps. 



Of the milk-teeth, the incisors in the upper jaw change first. 

 Of the molars, two are developed before the change of the 

 pre-molars. In the lower jaw the incisors change first, and 

 when two or three pre-molars have developed the last molar 

 has still to come. 



The arm-bone, or hwneriis, has one perforation ientepicondylar 

 foramefi) on its inner margin, and another above the joint 

 (except in Perodicticus). The bones of the fore-arm {radius 

 and ulna), and those of the leg {tibia and fibula) are net 

 co-ossified (except in Tarsius), so that the palm or sole can be 

 turned up at will. 



The bones of the digits are more or less flat and rounded 

 at the tips (differing in this respect from the Insedivora). One 

 of the ankle-bones, for the articulation of the opposable great 

 toe, the ento- cuneiform, as it is called, is rounded, as in the 

 Anthropoid Apes and Man. The thumb is opposable, but its 

 articulating bone in the wrist is not rounded, except in Avahis 

 and IndriSy which genera agree in this respect with Anthro- 

 popithecus and Man. The wrist has its central bone {os centrale) 

 present ; it is absent in Man and the higher Apes. 



The knee is free and not united to the side of the body by 

 integument. 



The two halves of the lower jaw are not always co-ossified (as 

 is the case in the Anthropoided). 



The opening in the base of the skull [the foramen rotundum) 

 which transmits from the brain a branch of the fifth nerve 



