CHAP, ii.] THE BRAIN. 1087 



675. In many animals in whom the sense of smell is acute, 

 a portion of the cortex, known as the " pyriform lobe " or " hippo- 

 campal lobule," and which is anatomically continuous with the 

 front end of the hippocampal gyrus (the part to which the name 

 uncinate gyrus is often restricted), acquires relatively large 

 dimensions. This arid the anatomical relations just mentioned 

 would lead us to suppose that a part of the cortex which is 

 continuous with the front end of the hippocampal gyrus is in 

 some way connected with smell. The argument from compara- 

 tive anatomy, however, is one which must be used with caution ; 

 since, besides the great difficulty of determining the homologies 

 of parts of the brain in different animals, relative increase in the 

 part in question might be correlated to other things than the 

 power of smell, and might be determined by circumstances having 

 no relation to smell. 



The experimental evidence, though on the whole it gives 

 support to the view, is conflicting; and when the difficulty of 

 determining whether a "dumb animal" can or cannot smell is 

 borne in mind, this will not .be wondered at. The observation 

 that electrical stimulation of the region in question gives rise to 

 movements of the nostrils, which have been interpreted as sniffing 

 in response to subjective olfactory sensations, cannot have much 

 weight; and while some observers have found that the removal 

 of this part of the brain destroys the sense of smell, others have 

 obtained negative results. 



The few clinical histories which bear upon the matter are 

 perhaps more trustworthy. These seem to shew that a lesion 

 involving the cortex of this region, but leaving the olfactory bulb 

 and tract, as well as other parts of the brain, intact, may destroy 

 or greatly impair smell. And we may perhaps give particular 

 weight to the cases in which epileptiform attacks, preceded by an 

 ' aura ' in the form of a peculiar smell, have been associated with 

 disease limited to this region ; for the phenomena of ' aura ' seem 

 to be connected with cortical processes. 



Though the evidence on the whole goes to shew that the 

 cortex at the front end of the hippocampal gyrus is especially 

 connected with smell, and we have so marked it in Fig. 132, yet 

 the whole matter stands on a somewhat different footing from 

 the sense of sight. In man the relations of smell to the other 

 operations of the brain (though, as we shall see in dealing with 

 the senses, somewhat peculiar) are far more limited than are 

 those of vision, and the psychical development of simple olfactory 

 sensations is extremely scanty. 



Sensations of Taste. 



676. This special sense though so closely associated with 

 smell stands, together with the special sense of hearing, on a 



F. 69 



