92 FOURTH GENERAL MEETING. 



This is a result very different indeed from that obtained if we 

 compare other mammals with one another. I cannot account for 

 that difference, except by postulating a much more considerable 

 increase of the folding of the cerebral cortex (and probably also of 

 that of the cerebellum) simultaneously with the increase of the size 

 of the body in Man than in the other mammals. Indeed, it is well- 

 known that the fissures on the surface of the cerebral hemispheres 

 in Man become more complicated, as the hemispheres are of larger 

 size. I was able to ascertain that this process really can account 

 for that considerable difference in the increase of the size of the 

 brain with the increasing bulk of the body, which we find to exist 

 between Man and the other mammals, but have now to refer to 

 my paper quoted as to the method applied. 



I only wish to point out that the claim made upon the size of 

 the cranium by the maxillary bones and the teeth as parts of the 

 masticatory apparatus seems to me to be the reason why in the 

 other mammals, contrary to Man, the adaptation of the brain to a 

 larger body is attained less by folding of the cerebral cortex than 

 by a real increase of the volume. It would be of no profit to Man 

 that the size of the skull should be enlarged in such a high degree 

 by the increasing brain. Man's already very much reduced maxillar 

 bone easily finds space necessary for its fixing on the cranium even 

 in the bulkiest individuals. A large cranium as such however is 

 certainly not profitable. Therefore the folding process of the 

 cerebral cortex progresses much faster with the increasing size of 

 the brain in Man than in the other mammals, and our exponent of 

 relation (r) ought to be a much smaller number. 



Though certainly the individual weight of the body in Man is a 

 very variable factor, modified not only by the changing contents of 

 the intestinal tractus, but also by the varying percentage of fat and 

 water of the body, if managed with care and taken as the average 

 from a certain number of individuals, as already has been pointed 

 out, it may still yield fair results. As would appear from some 

 comparisons it is a much more reliable basis of calculation than, for 

 instance, the height of the body or that of the trunk in Man. 

 Moreover, in Man only the fourth root of the body-weight ought to 

 be applied in the calculation, the influence of a deviation of the 

 body-weight on the result of the calculation being thus much 

 lessened. 



According to Dr Boyd's observations the average brain-weight 

 of 306 men aged from 20 to 50 years belonging to the working 

 classes in London was 1359 grammes, and the average body- weight 

 of 318 living Londoners aged from 23 to 50 years belonging to the 

 same classes, according to Dr Beddoe's tables, already quoted, was 

 61 kilogrammes. From these figures we now easily can calculate 

 an index of cephalisation. Doing the same from the brain-weight 

 of 364 South-German men as observed by Bischoff and from the 

 body-weight of 32 men belonging to the same nations I found quite 



