xi] 



centralis insulae); knowing then how closely olfactory cortex follows tin; rhinic fissure, and 

 looking upon the first part of the Sylvian fissure as really an offshoot of the rhinic, it 

 does not appear so remarkable that elements similar to those met with in the lobus pyri- 

 fonuis should be found in the lower and anterior part of the insula I refer to the 

 chromophilous fusiform evils, and particularly the smaller variety noticed in the region of 

 the "pole" of the island and reasoning on these lines it seems by no means impossible 

 that this is a relic of cortex which in lower creatures served for the treatment of olfactory 

 impressions. 



Failing this it is not impossible that the curious structure of the anterior insular 

 cortex as a whole is a display of specialisation for the elaboration of gustatory impressions, 

 and this possibility gains in likelihood when we take some experimental researches of 

 (lorschkow's into consideration, and also the point that the anterior insula is not far removed 

 from the cortex controlling movements of the tongue : . Gorschkow's statement based on no 

 less than 40 experiments on dogs, carried out in Professor Bechterew's laboratory, is that 

 the centre for the sense of taste occupies the convolutions lying immediately anterior to 

 the Sylvian fissure (gyms sylviacus anterior, gyrus ectosylvius anterior, and gyms com- 

 positus anterior); he infers that the centre is isolated, and that when these convolutions 

 are ablated, the sense of taste is abolished quite as purely and completely as is the sense 

 of smell when the destruction affects the lobus pyriformis. Homologising these results 

 Gorschkow places the human gustatory centre " in the region of the operculum " (details are 

 not given in the abstract which I have read). It is questionable, however, whether Gorschkow 

 is quite correct in this homology : unfortunately in the case of the dog there is no sulcus 

 diagonalis or other definable equivalent of the human anterior limiting sulcus of the 

 insula, but from what is known of the brains of other animals I think comparative anatomists 

 would have no hesitation in declaring that the gyri sylviacus and ectosylvius anterior come 

 within the insular limit (about the gyrus compositus anterior there would be doubt), and 

 therefore it would be more correct to say that the corresponding area in the human brain 

 is the anterior insula, not the operculum. 



It is freely acknowledged that the reasons for attributing a gustatory function to the 



anterior insula are far from strong, but the hypothesis is only submitted tentatively, and 



with the feeling that any data we can collect turning on the localisation of the sense of 

 taste are valuable. 



SUMMARY. 



1. The general fibre supply of the insular cortex is poor, and it likewise contains no 

 cells of large size. In the adult it is histologically separable into two main regions, an 

 anterior and a posterior, between which the sulcus centralis insulae roughly forms a 

 dividing line. 



2. The anterior region is distinguished by a weak definition of the line of Baillarger, 

 an absence of large fibres, two well-marked layers of elongated " large pyramidal cells " 

 separated by a faint stellate layer, and the presence in the inner of these two layers of 

 curious large chromophilous cells, of true spindle form, similar to cells noticed in the lobus 

 pyriformis and gyrus fornicatus. 



1 This implies that the mucous membrane of the tongue is specialised skin, and that the rule for sensory and 

 motor cortical centres for given parts to be deposited in approximation is followed. 



332 



