Address to the Anthropological Section / William Turner.

  • William Turner
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Address to the Anthropological Section / William Turner. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    21/25 page 20
    cortex of the human hrain, a third division—the association centres—is to he distinguished. Ii we compare the cerebrum in man and the apes, we find those convolutions which constitute the motor and sensory centres distinctly marked in both. An ape, like a man, can see, hear, taste, smell and touch; it also exhibits great muscular activity and variety of movement. It possesses, therel'oie, similar fundamental centres of sensation and motion, which are situated in areas of the cortex, resembling in arrangement and relative position, though much smaller in size than, the corre- sponding convolutions in the adult human brain. It is not unlikely, though the subject needs additional research, that the minute structure of these centres resembles that of man, though, from the comparatively restricted area of grey matter in the ape, the neuroues will necessarily be much fewer in number. In the cerebrum of a new-born infant, whilst the motor and sensory convolu- tions are distinct, the convolutions for the association areas, though present, are comparatively simple, and do not possess as many windings as are to be seen in the brain of a chimpanzee not more than three or four years old. Again, if we compare the brain of the Bushwoman, miscalled the Plottentot Venus, figured by Gratiolet and by Bischoffj or the one studied by Mr. John Marshall, with that of the philosopher Gauss, figured by Rudolph Wagner, we also recognise the convolutions in which the motor and sensory areas are situated. In all these brains they have a comparative simplicity of form and arrangement which enables one readily to discriminate them. When we turn, however, to the association areas in the three tiers of convolutions in the frontal lobe, and in the parieto- occipital and occipito-temporal regions where the bridging or annectant convolu- tions are placed, we cannot fail to observe that in a highly-developed hrain, like that of Gauss, the association convolutions have a complexity in arrangement, and an extent of cortical surface much more marked than in the Bushwoman, and to a still greater degree than in the ape. The naked-eye anatomy of the brain there- fore obviously points to the conclusion that these association areas are of great physiological importance. The problem which has now to be solved is the determination of their function. Prolonged investigation into the development and comparative histology of the brain will be necessary before W'e can reach a sound anatomical basis on which to found satisfactory conclusions. It will especially be necessary to study the suc- cessive periods of development of the nerve-tibre tracts in the cerebrum of apes and other mammals, as well as the magnitude and intimate structure of the association areas in relation to that of the motor and sensory areas in the same species. Flechsig, however, has not hesitated to ascribe to the association centres func- tions of the highest order. He believes them to be parts of the cerebral cortex engaged in the manifestations of the higher intelligence, such as memory, judgment, and retiection ; but in the present state of our knowledge such conclusions are of course quite speculative. It is not unlikely, however, that the impulses which are conveyed by the inter- mediate nerve-tracts, either on the one hand, from the sense centres to the associa- tion centres, or on the other, from the association centres to the sensory and motor centres, are neither motor nor sensory impulses, but a form of nerve energy, determined by the terminal connections and contacts of the nerve fibres. It is possible that the association centres, with the intermediate connecting tracts, may serve to harmonise and control the centres for the reception of sensory impressions that we translate into consciousness, with those which excite motor activitv, so as to give to the brain a completeness and perfection of structural mechanism, which without them it could not have po.ssessed. We know that an animal is guided by its instincts, through which it provides for its individual wants, and fulfils its place in nature. In man, on the other hand, the instinctive acts are under the influence of the reason and in'elligence, and it is possible that the association centres, with the iuteimediate association fibres which connect them with the sensory and motor centres, may be the, mechanism through which man is enabled to control his animal instincts, so far as they are dependent on motion and sensation.
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image