9 68 THE CENTRAL NERVOUS SYSTEM 



further source of fallacy is the fact that other sensations than those 

 of smell are caused by stimulation of the mucous membrane of the 

 nose. Substances like ammonia, for example, affect entirely the 

 endings of the trigeminus, which is the nerve of common sensation 

 for the nostrils. Pathological and clinical evidence would be of great 

 value, but it is as yet scanty, and of itself indecisive. Some cases 

 of epilepsy have been reported in which the attack was heralded by 

 smells for which there was no objective cause. At necropsy the un- 

 cinate gyrus was found diseased. So far as it goes, such evidence 

 supports the view derived from the anatomical connections of the 

 olfactory tracts, that the centre for smell is situated in the uncinate 

 gyrus on the mesial aspect of the temporal lobe, for the olfactory 

 track may be traced into this region. In animals with a very acute 

 sense of smell, this gyrus is magnified into a veritable lobe, called 

 from its shape the pyriform lobe; from its supposed function, the 



Fig. 396. Sensory Areas of Mesial Surface of Human Brain. The front of the brain 



is towards the right. 



rhinencephalon. The centre for taste is supposed to be situated in 

 the same region as the centre for smell (in the hippocampal convolu- 

 tion posterior to the uncinate gyrus). 



Ordinary and Tactile Sensations, including the muscular sense, 

 have been located in the Rolandic area (p. 963) ; and there are good 

 grounds for believing that afferent fibres from the joints, the muscles 

 and their accessory structures and the skin terminate here in arboriza- 

 tions which come into contact either with the motor pyramidal 

 cells, or with intermediate cells which link them to the pyKamidal 

 cells. 



Our knowledge of the localization of this group of sensations is still 

 unsatisfactory, largely because it has hitherto been necessary to rely 

 almost exclusively upon extirpation experiments, and it is difficult 

 to determine in animals the existence of a local defect of sensation due 

 to a limited cortical lesion. A promising new method, the application 

 of strychnine to limited regions of the cortex, seems likely to aid in 

 illuminating this dark corner of cerebral physiology (de Barenne). 

 Changes in cutaneous and deep sensibility of the fore-limbs of the cat 



