Page 412. 
144 THE BRAIN OF THE SUMATRAN RHINOCEROS. 
sumatrensis, although the greater size of the former species would 
have favoured an opposite conclusion. 
So complicated and numerous are the convolutions that the general 
type-plan of their disposition is to a considerable extent disguised. 
They very closely resemble the same in the Equide, as might have 
been surmised. The whole brain, however, is broader, especially near 
the posterior portion of the cerebral hemispheres, where the breadth 
is considerably greater than further forward. 
The accompanying diagram will facilitate the description. It re- 
presents the disposition of the main conyolutions upon the superior 
aspect of one hemisphere, and exhibits the direction of the sulci which 
divide them. Two diagonal sulci cut up the posterior part of each 
lobe into three oblique gyri, which may be called the (1) external, 
(2) middle, and (3) internal gyrus. The middle and internal of these 
fuse together near the transverse line which joins the two rudimentary 
Sylvian fissures, anteriorly to which there is, in the Equide, no indi- 
cation of further primary longitudinal division. The external oblique 
gyrus continues, from this line, directly forwards, and independent. 
Upper view of left cerebral hemisphere of Ceratorhinus sumatrensis, showing 
general direction of sulci. 
In Ceratorhinus sumatrensis the internal oblique gyrus is triangular 
in shape, its inner boundary being the great longitudinal fissure of the 
hemispheres, into which it descends a short distance. In the Equide 
the inner boundary of this gyrus is more superficial, and can be seen 
as a straight longitudinal line, just external to the fissure itself, in the 
superior view of the brain. The whole gyrus is much broken up by 
minor foldings of its elements, especially in its median portion, its 
outer moiety consisting of a minor gyrus, whose general direction is 
