CHAP, ii.] THE BRAIN. 795 



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 hav- 

 ing 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 4 aura ' in the form of a peculiar smell, have been associated 

 with disease limited to this region ; for the phenomena of 4 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. 137, 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. 



Serisations of Taste. 



502. This special sense though so closely associated with 

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

 different footing from the two preceding special senses, since the 

 nerves concerned belong to the category of ordinary cranial 

 nerves, and we lack, in reference to them, the anatomical lead- 

 ing which is offered to us in the case of the optic and olfactory 

 nerves. 



We shall see in dealing with the senses that the fifth nerve 

 and the glossopharyngeal nerve have been considered as nerves 

 of taste, but that the matter is one subject to controversy ; the 

 gustatory function of the fifth is attributed to the peculiar 

 chorda tympani nerve, and other questions have been raised. 

 Whatever view we take, however, the nerves of taste are ordi- 



