HUXLEY ON THE RELATIONS OF MAN TO THE LOWER ANIMALS. 79 



However, the citation from the Memoir of Schroeder van der Kolk and 

 Vrolik, given above, proves that in their opinion a rudimentary hippocam- 

 pus minor does exist in the Chimpanzee, and Dr. Allen Thomson adds his 

 valuable testimony in a still more decided manner to the same effect. 

 In the letter which I have already quoted, he says : — 



" I found an eminence in the floor of the posterior cornu and towards its inner side, 

 ■which I regarded as the hippocampus minor, and I found it produced exactly in the same 

 manner as in man, by the bulging into the ventricles of a portion of the brain, by a very 

 deep groove between the convolutions." 



In another letter (the 11th of iSTovember, 1860), replying to further 

 troublesome inquiries of mine, Dr. Thomson writes : — 



u I thought it best for my own satisfaction and yours, to open the lateral ventricle 

 from above, in a second brain which I possess. This brain, which was extracted from 

 a young animal in Africa, was placed in rum there, and it was both much discoloured 

 and not so well preserved as I could have wished. The appearances are, however, suffi- 

 ciently distinct to enable me to confirm entirely what I think I stated to you before, 

 viz. : 1. The prolongation of the cavity of the posterior cornu, to a considerable distance be- 

 yond the plane of the posterior edge of the corpus callosum (which, I presume, may be taken 

 as the best measure of the position of the parts); and, 2. The existence on the inner side, 

 and partly in the floor of that posterior cornu, of an eminence corresponding in all re- 

 spects with the hippocampus minor Just as I was setting about the 



examination of this point, I found an opportunity, in my dissecting-room, of looking at 

 a fresh human brain, and I thought it might be more satisfactory to examine the two 

 brains together. It so turned out, that the brain I cut in upon presented an example 

 (not uncommon) of great deficiency in the extent of the posterior cornu. I think it is 

 worth sending you a sketch of it, for it is really scarcely more developed than that of the 

 chimpanzee in this respect." 



Having now, as I trust, redeemed my pledge to prove that neither 

 the third lobe of the cerebrum, nor the posterior cornu of the lateral ven- 

 tricle, nor the hippocampus minor, are structures distinctive of and "pe- 

 culiar to the genus Homo," I may leave it to the reader to decide the 

 fate of the " sub-class Archencepliala" founded upon the supposed exis- 

 tence of these three distinctive characters. 



And here I might fairly leave the question ; but, essential as I have 

 felt it to be to my personal and scientific character to prove that my 

 public assertions are entirely borne out by facts, I am far from desiring 

 to deal with this important matter in a merely controversial spirit. 

 Therefore, although the differences hitherto referred to are certainly non- 

 existent, I proceed to inquire whether there are any other marked and 

 constant characters by which the human may be distinguished from the 

 Simian brain. 



Without doubt such characters are to be found; and in all probability, 

 as in the case of any other two distinct genera, the more carefully and 

 minutely our inquiries are carried out, the greater will be the number of 

 these differentiae. So far as my knowledge goes, the most prominent 

 and important are the following: — 



1 . In the anthropoid apes the brain is smaller, as compared with the 

 nerves which proceed from it, than in man. 



