280 ON THE RELATIONS OF MAN 



What may be the functional importance of either of these 

 structures we know not. 



As if to demonstrate, by a striking example, the impos- 

 sibility of erecting any cerebral barrier between man and 

 the apes, Nature has provided us, in the latter animals, 

 with an almost complete series of gradations from brains 

 little higher than that of a Rodent, to brains little lower 

 than that of Man. And it is a remarkable circumstance 

 that though, so far as our present knowledge extends, 

 there zs one true structural break in the series of forms of 

 Simian brains, this hiatus does not lie between Man and 

 the man-like apes, but between the lower and the lowest 

 Simians ; or, in other words, between the old and new 

 world apes and monkeys, and the Lemurs. Every Lemur 

 which has yet been examined, in fact, has its cerebellum 

 partially visible from above, and its posterior lobe, with 

 the contained posterior cornu and hippocampus minor, 

 more or less rudimentary. Every Marmoset, American 

 monkey, old-world monkey, Baboon, or Man-like ape, on 

 the contrary, has its cerebellum entirely hidden, posteriorly, 

 by the cerebral lobes, and possesses a large posterior cornu, 

 with a well-developed hippocampus minor. 



In many of these creatures, such as the Saimiri 

 (Chrysothrix), the cerebral lobes overlap and extend much 

 further behind the cerebellum, in proportion, than they 

 do in man (Fig. 16) and it is quite certain that, in all, the 

 cerebellum is completely covered behind, by well-developed 

 posterior lobes. The fact can be verified by every one 

 who possesses the skull of any old or new world monkey. 

 For, inasmuch as the brain in all mammals completely 

 fills the cranial cavity, it is obvious that a cast of the 

 interior of the skull will reproduce the general form of the 

 brain, at any rate with such minute and, for the present 

 purpose, utterly unimportant differences as may result 

 from the absence of the enveloping membranes of the brain 

 in the dry skull. But if such a cast be made in plaster, 

 and compared with a similar cast of the interior of a human 

 skull, it will be obvious that the cast of the cerebral chamber, 

 representing the cerebrum of the ape, as completely covers 

 over and overlaps the cast of the cerebellar chamber, 

 representing the cerebellum, as it does in the man (Fig. 20). 

 A careless observer, forgetting that a soft structure like the 

 brain loses its proper shape the moment it is taken out of 



