702 THE BRAIN. 



the vestibular division serves, as we have seen, for other functions than those 

 of hearing ( 555), but, as we shall urge in dealing with the senses, is not to 

 be regarded as wholly useless for the purposes of that sense. The cochlear 

 division we have traced ( 531) into the bulb, and the vestibular division 

 into the lateral auditory nucleus (which, perhaps, maybe regarded as a 

 continuation or segmental repetition forward of the cuneate nucleus or of 

 part of that nucleus), and into the cerebellum, the cerebellar continuation 

 being probably the part of the nerve which serves for coordinating func- 

 tions. The connections of the auditory nerve with the cerebral hemisphere 

 belong to the same category as those of other afferent cranial, and we may 

 add spinal, nerves; we have no very clear anatomical guide toward any 

 particular part of the cortex. 



When we turn to the empirical results furnished by experiment and 

 clinical observations, we find that these, though even less definite and less 

 accordant than in the case of the senses of sight and smell, point to part of 

 the first or superior temporal (temporo-sphenoidal) convolution (Figs. 149, 

 152, and 154) lying in the temporal lobe just ventral to the Sylvian fissure, 

 as being especially concerned in hearing in some such way as the occipital 

 lobe is concerned in vision. 



Electrical stimulation of this region of the cortex gives rise to " pricking 

 of the ears," and other movements such as are frequently connected with 

 auditory sensations ; but such phenomena are in this instance, perhaps, to 

 be depended upon even less than in other similar instances. While some 

 observers maintain that this convolution, the operation including other por- 

 tions of the temporal lobe as well, may be removed from a monkey without 

 producing any certain signs of deafness, other observers have found that 

 removal of it on one side affected the hearing of the ear on the opposite side, 

 and removal on both sides brought the animal into a condition in which, 

 without being, perhaps, absolutely deaf, it reacted toward sound in a very 

 imperfect manner indeed, very different from its normal behavior. The 

 scanty clinical histories bearing on this matter are not very decisive ; for 

 though deafness has been observed in connection with disease affecting the 

 superior temporal convolution, the lesion has usually invaded other parts as 

 well, and the deafness has been associated with other symptoms, notably 

 aphasia. An auditory " aura " has, however, at times been observed in con- 

 nection with disease of this region, as also a peculiar psychical failure, 

 known as " word-deafness," in which, though sounds are heard that is to 

 say, auditory sensations are felt, it may be even as usual the perception or 

 psychical appreciation of the sounds is lacking, and a spoken word is not 

 recognized. 



Lastly, we may add that though, as we said, the anatomical leading is 

 not definite, observers have found that in newborn animals, on the one 

 hand, destruction of the part of the cortex probably corresponding to the 

 region mentioned above leads to atrophy of the median corpus geniculatum, 

 and to some extent of the posterior corpus quadrigeminum ; and, on the 

 other hand, destruction of the internal ear leads to an atrophy of part of 

 the lateral fillet of the opposite crossed side, which may be traced to the 

 posterior corpus quadrigeminum ; and thence to the median corpus geuicu- 

 latum ; and section of the lateral fillet on one side leads, among other re- 

 sults, to atrophy of the striae acusticaB and tuberculum acusticum ( 531) of 

 the crossed side. This suggests that the path of auditory impulses is along 

 the cochlear nerve to the lateral fillet of the crossed side, and so by the pos- 

 terior corpus quadrigeminum and median corpus geniculatum to the cortex 

 of the temporal lobe of that crossed side, the two latter bodies bearing toward 

 hearing a relation somewhat like that borne toward sight by the anterior 



