September 26, 1901] 



NA TURh 



541 



questionably have had some influence in determining head- 

 forms, that I wish particularly to refer in this Address. 



The surface of the human cerebrum is thrown into a series of 

 tortuous folds or convolutions separated by slits or fissures, and 

 both combine to give it an appearance of great complexity. 

 These convolutions were long considered to present no definite 

 arrangement, but to be thrown together in the same meaningless 

 disorder as is exhibited in a dish of macaroni. During the 

 latter half, or rather more, of the century which has just ended 

 it has, however, been shown by the many eminent men who 

 have given their attention to this subject that the pattern which 

 is assumed by the convolutions, while showing many subsidiary 

 differences, not only in different races and different individuals, 

 but also in the two hemispheres of the same person, is yet 

 arranged on a con.sistent and uniform plan in every human brain, 

 and that any decided deviation from this plan results in an im- 

 perfect carrying out of the cerebral function. In unravelling the 

 intricacies of the human convolutionary pattern it was very 

 early found that the simple cerebral surface of the ape's brain 

 in many cases afforded the key to the solution of the problem. 

 More recently the close study of the manner in which the con- 

 volutions assume shape during their growth and development 

 has yielded evidence of a still more valuable kind. We now 

 know that the primate cerebrum is not only distinguished from 

 that of all lower mammals by the possession of a distinct occi- 

 pital lobe, but also by having imprinted on its surface a con- 

 volutionary design, which in all but a few fundamental details 

 is different from that of any other order of mammals. 



There are few matters of more interest to those anthropolo- 

 gists who make a study of the human skull than the relationship 

 which exists between the cranium and the brain during the 

 period of active growth of both. Up to the time immediately 

 prior to the pushing out of the occipital lobe, or, in other words, 

 the period in cerebral development which is marked by the 

 transition from the quadrupedal type to the primate type of 

 cerebrum, the cranial wall fiis like a tight glove on the surface 

 of the enclosed cerebrum. At this stage there would appear to 

 be a growth antagonism between the brain and the cranial 

 envelope which surrounds it. The cranium, it would seem, 

 refuses to expand with a speed sufficient to meet the demands 

 made upon it for the accommodation of the growing brain. In 

 making this statement it is right to add that Hochstetter, in a 

 carefully reasoned memoir, has recently cast doubt upon the 

 reality of the appearances which have led to this conclusion, 

 and at the recent meeting of the Anatomische Gesellschaft, in 

 Bonn, Prof. Gustaf Retzius,' one of the numerous observers 

 responsible for the description of the early cerebrum upon which 

 the conclusion is based, showed some inclination to waver in his 

 allegiance to the old doctrine. This is not the time or the 

 place to enter upon a discussion of so technical a kind, hut I 

 may be allowed to say that whilst I fully recognise the neces- 

 sity for further and more extensive investigation into this matter 

 I do not think that Hochstetter has satisfactorily accounted for 

 all the circumstances of the case. 



When the occipital lobe assumes shape the relationship of the 

 cranial wall to the encli sed cerebrum undergoes a complete 

 change. The cranium expands so rapidly that very soon a wide 

 interval is left between the surface of the cerebrum and the deep 

 aspect of the cranial envelope within which it lies. This space 

 is occupied by a soft, sodden, spongy meshwork, termed the 

 subarachnoid tissue, and it is into the yielding and pliable bed 

 thus prepared that the convolutions grow. At first the surface 

 of the cerebral hemisphere is smooth, but soon particular areas 

 of the cortex begin to bulge out and foreshadow the future 

 convolutions. These suffer no growth restriction, and they 

 assume the form of round or elongated elevations or eminences 

 which rise above the general surface level of the cerebral hemi- 

 sphere and break up its uniform contour lines in the same 

 manner that mountain chains protrude from the surface of the 

 globe. 



As growth goes on, and as the brain gradually assumes a bulk 

 more nearly in accord with the cavity of the cranium, the 

 space for surface protrusions of this kind becomes more limited. 

 The gyral elevations are now pressed together : they become 

 flattened along their summits, and in course of time they 

 acquire the ordinary convolutionary shapes. While this is going 

 on the valleys or intervals between the primitive surface eleva- 

 tions become narrowed, and ultimately assume the linear slit- 



1 Anatomisctie Gesellschaft. Bonn. May 21, igl?. Gustaf Relzius, 

 " Transilorische Furchen des Grosshirns." 



like form characteristic of the fissures. These changes occur 

 shortly before birth, but are not fully completed until after the 

 first few months of infancy. The final result of this process 

 is that the convolutions come into intimate relation with the 

 deep aspect of the cranial wall and stamp their imprint upon it. 



It is obvious that certain of the later changes which I have 

 endeavoured to]iortray might be ascribed to a growth antagonism 

 between the brain and the enclosing cranium at this period. In 

 reality, however, it is merely a process by which the one is 

 brought into closer adaptation to the other— a using up, as it 

 were, of superfluous space and a closer packing together of the 

 convoluti.-ins — after the period of active cortical growth is 

 past. Nevertheless the convolutionary pattern is profoundly 

 affected by it. and it seems likely that in this process we find the 

 explanation of the different directions taken by the cerebral fur- 

 rows in brachycephalic 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. We 

 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 interrupted form of fissural 

 development is one of the essential characteiistics 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 long 

 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 perfec- 

 tion 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 indicate certain of 

 the districts of cerebral cortex which have undergone a 'marked 

 increase in the human brain — an increase which may be reason- 

 ably 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 (i860, 

 1861, and 1S62) 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 

 Kingsley'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 Associa- 

 tion and declared that apes had ihippopotamus majors in their 

 brains just as men have. What a shocking thing to say ; for if 

 it were so, what would become of the faith, hope and charity of 

 immortal millions ? Vou may think that there are other more 

 important differences between you and an ape, such as being 

 able to speak, and make mschines, 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 Prof. 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 distinctive 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 297 



Orang • 232 



Man 21-2 



NO. 1665, VOL. 64] 



