v] ^4 General Consideration of Function 131 



Inspection of the diagrams in figure 11 representing the extent of the area on the mesial 

 ami Inferior surfaces of the brains of a chimpanzee and an orang, will show how closely 

 the anthropoid resembles the human arrangement; over the cuneus and along the lower and 

 .interior borders the agreement is exact; and again the visuo-psychic cortex, although it 

 may just spread over the upper lip of the stem of the calcarine fissure, does not extend 

 for any distance on to the free surface of the gyms fornicatus. 



On the lateral surface, this type of cortex closely embraces the visuo-sensory area, but 

 its relative width is not so great as it is in the human brain. The anterior boundary, on 

 account of its relation to the " Affenspalte," is the only limit which calls for special description. 

 Now along the dorsal margin of the hemisphere, it must be observed that the area is 

 found spreading on to the gyrus lying between the external prolongation of the parieto- 

 occipital fossa and the upper extremity of the " Affenspalte," a gyrus which seems to be 

 the equivalent of the human superior parieto-occipital annectant and which, in the case of 

 the orang's hemisphere represented, is curiously elongated, on account of the wide projection of 

 the parieto-occipital fossa. In thus spreading on to the superior parieto-occipital annectant 

 gyrus the human arrangement is copied, but here the resemblance ceases, for instead of 

 avoiding a definite and fixed relationship to named fissures, which we saw to be the case 

 in the human being, the anthropoid visuo-psychic area is given a sharp and definite boundary 

 in the great "Affenspalte." In all the three brains which I have submitted to examination 

 I have been careful to cut my serial sections of this region in the sagittal direction, in 

 order that the cortex coating the walls of the " Affenspalte " might be accurately studied ; and 

 in regard to the limits of the visuo-psychic type of cortex I have elicited the following 

 points of interest. In the upper half of the " Affenspalte," that is, in the portion lying central 

 to its junction with the ramus occipitalis of the iiitraparietal fissure, this type of cortex 

 clothes both walls and exhibits an inclination to spread forward over the anterior lip of 

 the fissure ; but in the lower or external half of the fissure, it is found only on the posterior 

 wall and does not reach to the floor. 



The lower or temporal division of the area presents no features of special importance, 

 it is not related to any fissures in particular and simply forms a skirt to the visuo-sensory 

 field. 



THE FUNCTIONS OF THE CALCARINE OR VISUO-SENSORY AND THE 

 OCCIPITAL OR VISUO-PSYCHIC FIELDS OF CORTEX. 



In the preceding pages, a detailed account of two types of cortical structure to be 

 found in the occipital lobe of both the human being and the anthropoid ape has been 

 given, also the exact limits and extent of the fields covered by these types of cortex have 

 been described, and since there is an abundance of experimental and clinical evidence 

 to prove that the visual function is localised in the occipital lobe, more especially in the 

 region of the calcarine fissure, it now remains for us to review this evidence with the 

 object of determining whether the areas, which I have mapped out on histological grounds, 

 represent the exact topography of the centres where visual sensations are received and in- 

 terpreted. 



For the sake of clearness, it will be advisable to consider the work which has been 

 done on visual localisation under three different headings, viz. (1) the experimental, (2) the 



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