100 ON CLASSIFICATION. 



Ill fact, even if the posterior cornu had not been demon- 

 strated (as it has now been) in the brain of numerous genera of 

 Apes, this one example would sufficiently demonstrate the asser- 

 tion, that the posterior cornu is " peculiar to the genus Homo" 

 to be simply untrue. 



Lastly, as regards the hippocampus minor — which is also said 

 to be " peculiar to man " — that structure is, as you perceive, as 

 distinct in the Orang's as in the man's brain, so that the third 

 term of the definition of the " Archencejyhala " is as contradic- 

 tory to plain fact as the other two (Fig. 40). 



Even were the posterior lobe, the posterior cornu, and the 

 hippocampus minor peculiar to man, as supposed by the definer 

 of the sub-class " Archencephala" instead of being, as they 

 really are, structures far better developed in some of the lower 

 apes than in him, their classificatory value would be extremely 

 doubtful, seeing that they are among the most variable of struc- 

 tures in the human brain. The casts upon the table of a Tartar's 

 and of an Australian brain-case will demonstrate to you how in- 

 significant may be the projection of the posterior lobe in one man 

 and how great it may be in another. While the practical anato- 

 mists and demonstrators whom I address will be familiar with the 

 singular variability of the posterior cornu and the hippocampus 

 minor — structures which, without any assignable cause, or 

 noticeable modification of the structure, or of the functions, of 

 the brain, may present every degree of development, from 

 absence to great size. 



So little, indeed, is any zoological value to be attached to 

 such a character as the degree of projection of the posterior 

 lobe, that closely allied apes present us with most singular dif- 

 ferences in this respect. Thus the group of South American 

 monkeys which comprises the Squirrel monkey (Chrysothrix), 

 the posterior lobes of whose brain project beyond the cerebellum 

 far more than they do in man, contains also the Howling monkev 

 (Mycetes), in which the posterior lobes cannot be said to project 

 at all. And within the last two days, Mr. Flower has discovered 

 (and the cast upon the table enables me to demonstrate the fact 

 to you) that in, at any rate, one species of Gibbon, the Siamang 

 (Hylobates Syndactylies) the cerebellum projects behind the pos- 



