492 ON THE RELATIONS OF MAN WITH THE LOWER ANIMALS 
lobes ; the singleness of the corpora candicantia ; the comparatively 
small and flat pons varolii ; the presence of corpora trapezoidea ; and, in 
the internal structure of the brain, the large size of the optic thalami in 
relation to the corpora striata, and the total absence of a posterior cornu 
to the lateral ventricle'—are all characters which are perfectly obvious, 
and which separate the brain of the Lemur as completely from that of 
Pithecus or Troglodytes, as from that of man. 
The description of the brain of Stenops tardigradus, by Vrolik, 
tells the same story even more strikingly; and the brains of 
Perodicticus and other Prosimize, exhibited in the Hunterian Museum, 
fully bear out the conclusion, that the vast differences noted obtain 
throughout the Prosimian division of the Quadrumana. 
M. Gratiolet, in fact, has been so struck by the immense discrepancy 
between the Simiz and Prosimiz in cerebral structure, that he proposes 
to consider the latter as forming a part of the order Insectivora. In this 
view he is at variance with all the other zoologists ; but, in order to meet 
all possible objections, I will, for the moment, suppose that he is right, 
and that the order Quadrumana should be restricted to the Simia. Even 
on this supposition, the force of my argument remains unchanged ; for 
the brains of the lower true apes and monkeys differ far more widely 
from the brain of the orang than the brain of the orang differs from that 
of man. Not only do they differ from the orang (and to a greater de- 
gree) in most of those respects in which the orang differs from man, but 
they present the absolute distinction, that while the orang, like man, 
has two corpora candicantia, the lower apes, like the other Mammalia, 
have only one. 
In respect of their cerebral characters, therefore, I hold it to be 
demonstrable that the Quadrumana differ less from man than they do 
from one another; and that, hence, the separation of Homo and 
Pithecus in distinct sub-classes, while Pzthecus and Cynocephalus are 
retained in one order, is utterly inconsistent with the principle of any 
classification of the Mammalia by cerebral characters. 
Ona future occasion I propose to take up the question, whether, on 
other grounds, there is any reason for departing from the Linnean view, 
that man is to be regarded asa genus of the same order as that which 
contains the Quadrumana. 
1 «Cornu posterius in Simiis et Phocis brevissimum et vix conspicuum est: in ceteris 
mammalibus plane desideratur.”—Icones, p. 54. 
