/ Lll 



REPORT — 1901. 



explanation of the different directions taken by the cerebral furrows in bracbr- 

 cephalic and dolichocephalic heads. 



The cortical elevations which rise on the surface of the early cerebrum are due 

 to exuberant growth in localised areas. There cannot be a doubt that the process 

 is intimately connected with the development of function in the districts concerned, 

 AVe know that functions of different kinds are localised in different parts of the 

 cortex, and when we see an area on the surface of the early cerebrum rise up in 

 the form of an eminence we may reasonably conclude that the growth in the area 

 concerned is the structural foundation of what will become later on a centre of 

 functional activity of an acute kind. 



A consideration of this matter gives the clue to the simple convolutions of the 

 ape and the complex convolutions of man, and, further, it explains how the inter- 

 rupted form of fissural development is one of the essential characteristics of the 

 human brain as compared with the simian brain. Areas which rise up in the 

 form of one long elevation on the surface of the ape's brain appear in the form of 

 several eminences on the surface of the human brain, and fissures which appear 

 in the form of loug continuous slits in the simian cerebrum appear in the human 

 cerebrum in several detached bits, which may or may not in the course of time 

 run into each other and become confluent. All this is due to the greater definition, 

 refinement, and perfection of the functions carried on in the cerebral cortex of 

 man. It is an index of a more complete 'physiological division of labour' in the 

 human brain. 



It is not necessary, for the purpose I have in view, to enter into any detail 

 regarding the many points of difference which become evident when the cerebral 

 surface of the ape is compared with that of man. It is more my purpose to indi- 

 cate certain of the districts of cerebral cortex which have undergone a marked 

 increase in the human brain — an increase which may be reasonably supposed to 

 be associated with the high mental attributes of man. To us, at the present time, 

 it is difficult to conceive how it was ever possible to doubt that the occipital lobe 

 is a distinctive character of the simian brain as well as of the human brain, and 

 yet at successive meetings of this Association (1860, 1861, and 1862) a discussion, 

 which was probably one of the most heated in the whole course of its history, took 

 place on this very point. One of our greatest authorities on animal structure 

 maintained that the occipital lobe and the hippocampus minor — an elevation in its 

 interior — were both peculiar to man and to him alone. Everyone has read in the 

 ' Water Babies ' Charles Kings'ey's delightful account of this discussion. Speaking 

 of the Professor he says : ' He held very strange theories about a good many 

 things. He had even got up at the British Association .ind declared that apes 

 had hippopotamus majors in their brains just as men have. AVhat a shocking 

 thing to say ; for if it were so, what would become of the faith, hope, and charity 

 of immortal millions? You may think that there are other more important 

 differences between you and an ape, such as being able to speak, and make 

 macliines, and know right from wrong, and say your prayers, and other little 

 matters of that kind ; but that is a child's fancy,' In the light of our present 

 knowledge we can fully understand Professor Huxley closing the discussion by 

 stating that the question had * become one of personal veracity.' Indeed, the 

 occipital lobe, so far from being absent, is developed in the ape to a relatively 

 greater extent than in man, and this constitutes one of the leading positive dis- 

 tinctive characters of the simian cerebrum. Measured along the mesial border, 

 the percentage length of the occipital lobe to the total length of the cerebrum in 

 the baboon, orang, and man is as follows : — 



Baboon 29-7 



Orang 23-2 



Man 21-2 



But these figures do not convey the full extent of the predominance of 

 the occipital lobe in the ape. The anterior border of the lobe grows forwards 

 beyond its proper limits, and pushes its way over the parietal lobe which lies in 

 front, so as to cover over a portion of it by an overlapping lip termed the occipital 



