THE LEMURS. 9 
closed in by bone behind (as in Monkeys), but freely communi- 
cating beneath the post-orbital process (except in Zars¢us) 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 12, C+, P3, M2= 36 (zvde antea, p. 6), and the upper 
jaw hasa toothless space in the centre (except in the Aye-Aye). 
Of the upper teeth, the zzctsors are sometimes absent, but 

Fig. 3. Foot of Chirogale trichotis, Giinther. 
(P..Z. Ss, 1875, pao) 
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 cingulum, 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 
