48 ON THE AFFINITIES AND DIFFERENCES BETWEEN THE 



answer will be in the negative; the application of such an ad- 

 mission to further argument I leave to suggest itself. 



The two cerebral hemispheres, with the internal and external 

 anatomy of which we have so long been dealing, might well bear 

 some other name than hemisphere, for, according to results of 

 experiments performed pathologically, for us, either by accident or 

 disease, they are not so much parts of one whole as two organs 

 mutually supplementing each other's meanings, in the same manner 

 as any of the numerous sets of paired organs in our bi-laterally 

 symmetrical bodies. Still, as '.vis unita fortiori there is an appara- 

 tus in the brain for enabling the two distinct organs which its 

 hemispheres, or rather ovoids, make up, really to act as if they 

 were halves of one whole. This apparatus consists of various longi- 

 tudinal and transverse connecting bars and floors, between what 

 would be in the adult animal, as in lower and developing organisms, 

 easily divaricable, albeit apposed masses. The most important of 

 these, in a physiological point of view, is the corpus callosum. 

 It roofs over the ventricles ; it is continuous with the fibres of 

 the now familiar hippocampus minor ; it binds together both 

 the ovoids during life, as it prevents them utterly falling apart 

 after death. (See Figs, t a, I b, 2.) It is all but, if not entirely, 

 fibrous, inter-nunciant ; it transmits ; it cannot originate ; its in- 

 crease of bulk may be supposed to depend considerably upon in- 

 crease of use, for in the child it is but one-half (or less) the length 

 of what it is in the adult, increasing, it may be, from as little 

 as if to 4 inches. The relation of length in the monkey may be 

 gathered from the diagram (Fig. i b). It is seen not to extend as 

 far back as two shaded nodules ; in the human brain it projects 

 beyond. A more careful and searching examination 1 has shown 

 that its sectional area, in relation to the ovoids it binds together, is 

 in the ape but half of that of the same structure in the same 

 relations in man. This, again, is but a difference of degree, but it 

 is a real difference, albeit clearly of physiological rather than of 

 serial importance. 



Our final enquiry will be, what is the weight of the entire nerve 

 mass contained within the ape's brain-case, and what is the weight 

 of the human encephalon ? This weight is either absolute, what the 



1 ' Nat. Hist„Review,' July, 1861, 'On the Brain of a Young Chimpanzee,' by J. 

 Marshall, Esq., F.R.S. 



