496 ON THE BRAIN OF ATELES PANISCUS 
the Dog, on the contrary, the internal surface of the occipital bone 
below the tentorium is much excavated ; and, when the palate was 
horizontal, the posterior edge of the cerebellum must have projected 
far beyond the cerebral lobes. 
In Lemur catia the inclination of the tentorial plane is hardly 
greater than in J/ycetes ; but if the palatal line be made horizontal, it 
will be found that the posterior boundary of the cerebellar chamber 
projects for th of an inch beyond that for the cerebrum, although the 
greatest length of the cranial cavity is only 1°9 inch. In fact, the 
cerebral hemispheres of the Lemur have a less backward develop- 
ment than those of the Dog. I believe that all the Lemurs are in the 
same case, and that the Prosiwz@ are sharply defined from the Sze 
by the fact of always having more or less of their cerebellum 
uncovered ; so that, by this character alone, the Lemurine brain is far 
more widely separated from that of any Simian, than the latter is 
from the human brain. 
While one American Monkey (JZyeetes) is, if the development of 
its posterior lobes only be taken into account, at the bottom of the 
series of Szz@, if the same character alone be considered, another 
Simian, inhabiting the same geographical area, is at the top; I refer 
to Chrysothrtx sciureus, whose posterior lobes, as I. G. St.-Hilaire long 
ago proved, are better developed than those of any other Mammal, 
overlapping the cerebellum by one-fifth of their length. In fact, if 
the Primates were arranged according to the development of their 
posterior cerebral lobes we should have some such descending series 
as the following :—Czhrysothrix, Cebus, Troglodytes, Man,... . 
.l/ycetes—a series which sufficiently illustrates the classificatory value 
of these structures. So much for the posterior lobe. I turn now to 
the next point, the demonstration of the existence of the posterior 
cornu in A¢eles. 
When the lateral ventricle was exposed in the ordinary way 
(Pl. NXIX. [Plate 36] fig. 5) a straight line passing from the ex- 
tremity of the anterior to that of the posterior cornu measured 2°1 
inches. A distance of 1°3 inch separated the anterior end of the 
anterior cornu from the commencement of the descending cornu ; 
while a straight line extending from the commencement of the 
descending to the end of the posterior cornu measured 0°75. Each 
lateral ventricle, measured from the centre of the corpus callosum ta 
the outer boundary, at its widest point, or opposite the commence- 
ment of the descending cornu, was about half an inch wide. The 
posterior cornu has a general direction backwards, outwards, and then 
1 See the ‘ Zoologie du Voyage de la Vénus’ for an excellent figure of this brain. 
