282 Tltc Homologies of the Lititbic Lobe 



this so-called " lateral " sulcus, instead of forming a rough outer boundary to the area, as it does 

 in Felis and Canis, lies wholly within the field. For this reason I cannot help thinking that it is 

 the direct homologue of the marginal or suprasplenial fissure in other animals, and that to label 

 it lateral is an error. 



So far as I can judge, the study of the occipital lobe in these animals provides no direct 

 information on the genesis of the " Affenspalte." 



I feel that little is to be gained by comparing the histological results bearing on the cortical 

 localisation of the visual function with those obtained by the experimenter. Invaluable service 

 was rendered by the physiologist when he indicated that sight was centred in the occipital lobe, 

 but his methods were necessarily crude I refer particularly to ablations and now that we have 

 such strong proof that the cortex, to which visual impulses stream, is possessed of a distinctive 

 structure, I am sure the advantage held by the microscope over the scalpel, as a discriminating 

 agent, will be allowed. Only one point calls for comment. In the brain of Homo and the higher 

 ape I have mapped out an area investing the visuo-sensory field, or area striata, to which I have 

 given the designation visuo-psychic, in the belief that it is intended for the further elaboration of 

 impulses primarily received in the first-named area. But, distinctive as the structure of this 

 cortex is in Primates, it is a remarkable truth that a corresponding area baffles definition in the 

 lower animals; only in Canis, and then along the very outskirts of the area striata, have I seen a 

 structural arrangement reminding me of such cortex'. 



o O 



It appears therefore that this cortex is almost entirely a neopallic formation. 



LOBUS PYRIFORMIS. 

 ffippocampal region. 



The changes undergone by the lobus pyriformis, in its passage from the macrosmatic to the 

 microsmatic condition, have been so thoughtfully and accurately studied by comparative anatomists 

 that my histological examination of the part, complete as it has been, only yields a confirmatory 

 repetition of previously published results. With the elongation and attenuation of the olfactory 

 peduncle, the deepening of the sulcus olfactorius, the flattening and reduction in size of the 

 tuberculum olfactorium, the disappearance of the anterior limb of the rhinal fissure, the bending 

 of the pyriform lobe to produce the vallecula Sylvii, the diminution in relative bulk of the caudal 

 portion of the pyriform lobe, we are familiar, as well as satisfied that all these events have been 

 given a correct interpretation. And although I have been successful in identifying the various 

 types of cortex previously seen and studied in the human brain, and have added something to 

 our knowledge, by showing their exact distribution in some macrosmatic brains, the result unfor- 

 tunately does not bring us any nearer understanding the true physiological significance of these 

 remarkable territorial variations in structure 2 . 



LIMBIC CORTEX. 



As with the lobus pyriformis, so with the gyrus fornicatus, the facts point to its being invested 

 by cortex of great phylogenic age. It seems to have an advantage over the lobus pyriformis, 

 inasmuch as it has maintained a better pitch of morphological representation through the different 

 cycles of brain growth. 



1 It is of some interest to note that the circle of cortex, destruction of which gave rise to "psychical blindness" 

 (Seelenbliudheit) in the dogs operated upon by Hunk, takes in the outskirts of the area striata. 



- The types of cortex to which I drew attention were, (1) that on the lobus pyriformis, (2) that covering the 

 wall of the fissura hippocampi, (3) that seen in the gyrus deutatus, and (4) the rudimentary cortex on the tuberculum 

 olfactorium. 



