506 PHYSIOLOGY 



as the lateral fillet. The fibres of this tract end 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 lobe. 



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 con- 

 volution causes deafness, but Schafer found that, even after extir- 

 pation of the superior temporal convolutions of both sides, monkeys 

 showed signs of hearing quite distinctly, and of understanding 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 

 convolution, 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 perception, are found almost invariably 

 to be closely associated with the superior temporal convolution. 



SMELL AND TASTE 



The course of the fibres from the olfactory lobe may be used 

 to throw light upon the localisation of olfactory sensation in the 

 cerebral cortex. There is a great divergence between different 

 animals in the degree to which the olfactory sense is developed, 

 and with this divergence we find corresponding variations in the 

 development of certain portions of the brain. In those species with 

 highly developed olfactory sense the following parts of the brain 

 show special growth : 



(1) The olfactory lobe, including the olfactory bulb, and the 

 olfactory tract. 



(2) The posterior part and the inferior surface of the frontal lobe. 



(3) The hippocampal gyrus and the dentate convolution. 



(4) A convolution termed the bordering gyrus and forming that 

 part of the gyrus fornicatus closely encircling the corpus callosum. 



(5) The anterior commissure. 



The olfactory lobe is connected almost exclusively with the cerebral 

 hemispheres of the same side. Ferrier found that electrical excitation 

 of the hippocampal region causes contortion of the lip and nostril on 

 the same side, i.e. a reaction such as that actually induced in these 

 animals by application of an irritative or pungent odour direct to the 

 nostril. Ablation experiments have not yielded very definite evidence 

 on the question of localisation of the olfactory sense. So widespread 

 are the connections of the olfactory tract throughout the brain that 



