THE LEMURS. 9 



closed in by bone behind (as in Monkeys), but freely communi- 

 cating beneath the post-orbital process (except in Tarsius) with 

 the temporal hollow behind. In the young of some species the 

 orbit is more enclosed than it is in the adult : the orifice for the 

 lachrymal duct of the eye is placed external to the margin of 

 the orbit : the hollow for the olfactory lobes of the brain is 

 always large. 



Having four kinds of teeth, and a set in succession to the 

 milk-teeth, they are Heterodont and Diphyodont. The dental 

 formula is If, C|, P|, Mf = 36 (vide antea, p. 6), and the upper 

 jaw has a toothless space in the centre (except in the Aye- Aye). 

 Of the upper teeth, the incisors are sometimes absent, but 



Fig. 3. Foot of Chirogale trichotis, Giinther. 

 (P. Z. S., 1875, p. 79.) 



generally present ; if unequal in size the inner one is the larger 

 of the two. The canines are prominent ; the pre-molars all have 

 a a'ngu/um, or girdle, round the base, more or less enlarged 

 backwards into a process ("talon" or "heel"); the anterior 

 pre-molar vertically long and canine-shaped ; the median and 

 posterior with three main points (tubercles or cusps) and one 

 or two smaller ones on the crown, and having a bar or ridge 

 uniting the front inner with the hind outer cusp. The anterior 

 and median molars have three or four main cusps, and one 



