750 A MANUAL OF PHYSIOLOGY 



called 'word deafness,' which will be referred to directly 

 (P- 753)- I* 1 deaf-mutes the first temporal convolution may 

 be atrophied. There is evidence that the posterior corpora 

 quadrigemina and the mesial geniculate body form an 

 inferior relay on the route between the fibres of the auditory 

 nerve and the temporal cortex. There are indications that 

 within the auditory area so-called ' musical centres ' exist 

 that is, an orderly arrangement of the cell-bodies of the 

 neurons that have to do with the perception of pitch, so that 

 a limited lesion may cause deafness to notes of a particular 

 pitch when it is situated in one part of the area, and deaf- 

 ness to notes of a different pitch when it is situated else- 

 where (Larionow). 



Centre for Smell. As to the position of the centre for 

 smell, direct experiment on animals cannot teach us much, 

 for if the outward tokens of visual and auditory sensations 

 are dubious and fluctuating, still more is this the case with 

 the signs of sensations of smell. A 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. So far as it goes, however, it undoubtedly sup- 

 ports 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 tract 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 rhinen- 

 cephalon. The centre for taste is supposed to be situated 

 in the same region as the centre for smell. 



Ordinary and tactile sensation have been located by some 

 observers on the mesial surfaces of the hemispheres in the 

 hippocampal convolution and the gyrus fornicatus. But this 

 cannot be considered as settled, and in any case this is not 

 the only region where common sensibility is represented. 



