Lesem, Fore-Brain of Macacus. 7 
extends from the genu of the corpus callosum to the lower 
border of the splenium. Here it becomes the hippocampal 
gyrus. The latter is limited above by the collateral sulcus. In 
Macacus as in man the hippocampal gyrus forms a convolution 
of the temporal lobe, and is fused with the rest of hemisphere. 
In the brain of the sheep this is not the case; the hippocampus 
has no connection whatsoever with the exterior of the brain. 
In Quain’s ‘‘Anatomy of the Human Brain’ BEEvor is quoted 
as saying that the hippocampus major of apes receives no 
fibres whatsoever from the lyra of the fornix. To determine 
this point I carefully dissected two brains of Macacus and 
found in both a distinct band of fibres running from the lyra of 
the fornix to the hippocampus major, 
The island of Reil in Macacus consists of two convolu- 
tions derived from the orbital surface of the frontal lobe. As 
in man the insula is overlapped by the operculum, and is thus 
invisible on the exterior of the undissected brain. In carni- 
vores owing to the non-development of a large temporo- 
sphenoidal lobe, no insula exists. 
The Lateral Ventricles. 
The lateral ventricles of Macacus are especially interesting 
owing to the enormous extent to which the posterior cornu is 
developed. This development is not uniformly attained by 
man. Numerous cases are on record where the posterior 
cornu has been of small size or rudimentary. In the past year 
I have seen two brains, one that of a child two years old, the 
other an adult brain of thirty years, in which the posterior 
cornu of the left side measured 1.5 cm. and 2 cm. respectively. 
The right posterior cornu was well-developed in both cases. 
The posterior horn of Macacus presents a well-developed bulb, 
but an ill-developed calcar avis. The anterior and the descend- 
ing cornua present no features markedly different from those 
of man. 
The corpus striatum of Macacus is remarkable in that the 
lenticular nucleus seems to exceed the caudate in size. As in 
man the lenticular nucleus consists of three parts, an outer 
