vii J Lhiihlf Lobe and Olfactory Area 189 



that a comparison of the histological structure of the linibic lobe in the simian and human 

 brains fails to disclose differences of marked importance. 



As regards the structure of the lobus pyriformis we have already emphasised Un- 

 importance of the rudimentary fissura rhinica as a histological boundary in the human brain. 

 Now comparative anatomists have shown that in the anthropoid brain this fissure is retained 

 in its entirety a truth which is amply confirmed by the three specimens which have come 

 into my possession and on examination of the cortex we get a repetition of the proof of 

 the stability of this fissure as a histological landmark. In structure the cortex of the lobus 

 pyriformis also has a human appearance ; just beneath the surface the groups of large 

 polymorphous cells are reproduced and the fibre-elements exhibit a similarity of arrangement 

 in support of the homology. 



The lamina medullaris externa of the fissura hippocampi appears to be deeper and 

 denser, and perhaps more extensive, in the ape than in man. 



The difference in character between the deep, large, pyramidal cells of the cortex of 

 the fissura hippocampi and the large cells of the gyrus dentatus is more clearly illustrated, 

 and it seems that the latter cells, and certainly those of the stratum granulosum of the 

 cornu ammonis, exhibit a higher pitch of development in these animals than they do in man. 



As the gyrus semilunaris of Retzius is concealed from view by the infolding of the 

 brain in this situation and as all these specimens had been hardened before reaching my 

 hands, I have been unable to determine whether this gyrus is represented in the anthropoid 1 , 

 and lacking orientation details afforded by a preliminary anatomical examination, I am 

 obliged to withhold any statement concerning its structure. 



The striae medullares appear to possess a degree of representation equivalent to that 

 of man, and they have similar connections anteriorly and posteriorly with the septum 

 pelluciduni and gyrus dentatus respectively. 



The gyrus subcallosus is a trifle richer in fibres than it is in man. 



The gyrus fornicatus is again distinguishable by the relatively small size of its contained 

 nerve fibres and cells, a feature which is especially noticed in the cortex of the callosal 

 lip and wall. On the floor of the callosal fissure around the splenium there is a localised 

 thickening of the zonal layer, but it is more restricted in extent than the corresponding topical 

 variation in the human brain. 



Without examining more material I should not like to say whether the perigenual 

 area which in the human being is characterised by the presence of moderately large and 

 deeply placed chromophilic cells, is represented in the anthropoid. As the cortical cells of 

 the anthropoid are, relatively speaking, all small, judgment concerning their colour-reaction 

 is made difficult. 



A GENERAL CONSIDERATION OF THE FUNCTIONS OF THE LIMBIC LOBE. 



Clinico-pathologists, experimenters, and comparative anatomists have all in turn attempted 

 to decide the functions of the various parts included in Broca's limbic lobe, and the broad 

 results to be gathered from their researches collectively are that certain parts of the lobe 

 preside over the functions of taste and smell, but it is still a debateable matter what parts 



1 The gyri semilunaris and circumambiens have been seen in some of the lower apes (Gustav Retzius and 

 Elliot Smith). 



