28 ON THE AFFINITIES AND DIFFERENCES BETWEEN THE 



that the same parts exist as in the vervet and in man is plain 

 enough, in all three alike is there a triply-divided ventricular 

 cavity, but relatively the posterior compartment is enormously larger 

 in the American monkey, and the now notorious hippocampus 

 minor it contains is enormously larger also than the homologous 

 structures in either of the two brains between which it stands. 

 The third cornu or horn in the marmoset is a bay in comparison 

 with the other two cornua, and they are in relation to it but creeks 

 and inlets ; the relations of the three compartments are entirely 

 reversed. The hippocampus minor is a huge island ; the hippo- 

 campus major but a boomerang-shaped reef; the relations of the 

 contained parts are entirely reversed also. As the facts, then, of 

 comparative anatomy stand, the semi-simious marmoset has, rela- 

 tively to its size, a larger hippocampus and a larger posterior 

 division of its ventricular cavity than has the true Simiada, Cerco- 

 pithecus lalandii ; the Cere opt thecus lalandii has a larger hippocampus 

 minor and a larger posterior cornu than has man himself. So 

 much for what is called the serial or classificatory value of these 

 structures as differentiating us from the lower animals. Two words 

 upon their physiological importance. The dog is gentle and docile, 

 capable of education and of forming attachments, yet he lacks 

 obviously what the ape as obviously possesses. Secondly, a glance 

 at a rabbit's 1 brain (similarly dissected) will show, when compared 

 with that of the dog's, that the ventricular cavity has encroached 

 upon and eaten away what in its canine enemy is a solid mass of 

 nerve matter. A large cavity is correlated with little neurine, but 

 the neurine, and not the ventricular cavity, is what the mind works 

 with. Basing one's hopes and trust upon neurine and hippocampi is 

 basing them upon something solid, even though it be but sand ; 

 basing them upon a ventricle's creek is but basing them upon the 

 sea. 



The hippocampi have always been dangerous ground for the 

 anatomist, the hippocampus major in days gone by, as the hippo- 

 campus minor in our own. The boomerang-shaped body so visible 

 and so vertical in the dog's brain, plain, but not so plain, because 

 more horizontal in the simious and human encephala, is the hippo- 

 campus major ; an indentation in the drawing from the human 



1 My attention was drawn to this point by Charles Robertson, Esq., of the 

 University Museum. 



