794 OLFACTORY SENSATIONS. [BOOK in. 



vision the cortical events are psychical in nature, and that the 

 function of the optic radiation is to furnish what we may call 

 crude visual sensations for further psychical elaboration. Or 

 perhaps we do wrong in attempting to dissociate in any such 

 distinct way the cortical and the tegmental events. The re- 

 markable dependence as regards nutrition between the occipital 

 cortex and the tegmental masses, of which we spoke a little 

 while back, shews that the two work together in the closest 

 way. Possibly we are wrong in thinking that in the generation 

 of a visual sensation, a something passing upwards from the one 

 is transformed into something else in the other, and ought 

 rather to suppose that the sensation is a product of the two 

 working together in a manner to the understanding of which 

 our ordinary conceptions of nervous impulses gathered from 

 the study of ordinary efferent and afferent nerves afford us 

 little help. Possibly also the ties between the cortical and 

 tegmental processes are drawn tighter in the higher animals 

 as vision becomes more complex, so that after total removal of 

 the cerebral cortex while the bird and possibly even the dog 

 may be said still to 'see,' man and probably the higher monkeys 

 appear, as experiments and clinical histories shew, to be not 

 only psychically but in every way blind, and that long before 

 degenerative changes in the tegmental masses can have become 

 marked. 



As to the several parts played by the individual tegmental 

 masses we at present know little or nothing. It is worthy of 

 note that when we compare various animals, we find that the 

 connections of the cortex with the corpus quadrigeminum are 

 the more prominent in the lower animals, and in the higher 

 animals more and more give place to those with the pulvinar 

 and especially with the corpus geniculatum. Some facts per- 

 haps may be taken as indicating that the corpus quadrigeminum 

 is especially concerned, when visual sensations influence the 

 coordination of movements ; but this is not certain. 



Sensations of Smell. 



501. In many animals in whom the sense of smell is acute, 

 a portion of the cortex, known as the ' pyriform lobe ' or ' hippo- 

 campal lobule,' and which is anatomically continuous with the 

 front end of the hippocampal gyrus (the part to which the name 

 uncinate gyrus is often restricted), acquires relatively large 

 dimensions. This and the anatomical relations just mentioned 

 would lead us to suppose that a part of the cortex which is 

 continuous with the front end of the hippocampal gyrus is in 

 some way connected with smell. The argument from compara- 

 tive anatomy, however, is one which must be used with caution ; 

 since, besides the great difficulty of determining the homologies 



