448 



PHYSIOLOGY 



faces of the occipital lobes, and we find the same relative limitation of area 

 as we proceed from lower to higher forms in the case of the other sensory 

 areas of the cortex. 



THE AUDITORY AREA 



Anatomical study indicates a connexion of auditory sensations with the 

 superior temporal lobe. The impulses, started by the arrival of sound waves 

 at the ear, travel by the cochlear nerve to the medulla. From the two audi- 

 tory nuclei a well-marked set of fibres passes across to the opposite side in 

 the corpus trapezoides, then turns up into the tegmentum of the opposite side 

 to form the tract known as the lateral fillet. The fibres of this tract end 



FIG. 233. Perimeter charts from right and left eye, showing the limitation of the field of 

 vision (right hemianopia) produced by a lesion of the left occipital cortex. (BK< HTKKKW.) 



partly in the inferior corpora quadrigemina, partly in the internal geniculate 

 body. From the latter, fibres pass into the internal capsule, and thence as 

 'auditory radiations' directly to the superior temporal convolution. 



In the monkey stimulation of the upper two-thirds of this lobe of the 

 brain causes pricking of the opposite ear, dilatation of the pupils, and rotation 

 of the head and eyes to the opposite side. It was stated by Ferrier that 

 ablation of the superior temporal convolution causes deafness, but Schafer 

 found that, even after extirpation of the superior temporal convolutions of 

 both sides, monkeys showed signs of hearing quite distinctly, and of under- 

 standing the nature of the sounds heard. One must conclude therefore that 

 the function of auditory perception is not entirely confined to the temporal 

 lobe, though its focal point may be located in the superior temporal con- 

 volution, especially in that part which is seated within the fissure of Sylvius. 

 This conclusion is strengthened by the results of clinical evidence in man, in 

 whom cerebral lesions, which have produced disturbances of auditory per- 

 ception, are found almost invariably to be closely associated with the superior 

 temporal convolution. 



