VISUAL AND OTHER SENSATIONS. 701 



determining the homologies of parts of the brain in different animals, rela- 

 tive 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 won- 

 dered at. The observation that electrical stimulation of the region in ques- 

 tion 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 show 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, per- 

 haps, give particular weight to the cases in which epileptiform attacks, pre- 

 ceded 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 show that the cortex at the 

 front end of the hippocampal gyrus is especially connected with smell, and 

 we have so marked it (in Fig. 155), yet the whole matter stands on a some- 

 what 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 deal- 

 ing 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. 



588. 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 cate- 

 gory of ordinary cranial nerves, and we lack, in reference to them, the ana- 

 tomical leading 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 

 glosso-pharyngeal 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- 

 nary cranial nerves, and we have no anatomical guidance as to the fibres of 

 either of the above two nerves making special connections with any part of 

 the cortex. Though sensations of taste enter largely into the life of ani- 

 mals, and, indeed, of man himself, we have no satisfactory indications which 

 will enable us to connect this special sense with any part of the cortex ; the 

 view, indeed, has been put forward that some part of the cortex in the 

 lower portion of the temporal lobe, not far from the centre for smell, serves 

 as a centre for taste ; but the arguments in favor of this view are not, as 

 yet at least, convincing. 



Sensations of Hearing. 



589. The cochlear division of the eighth or auditory nerve may be 

 assumed to be a nerve of the special sense of hearing, and of that alone ; 



