ON THE FUNCTIONS OF THE CEREBRUM 299 



the histological but also' the clinico-anatomical and experimental 

 aspects, and contains a mass of interesting information. The author 

 describes the visual cortex of the insectivora, rodents, marsupials, 

 ungulates, carnivora, lemurs, and primates. He arrives at the 

 following conclusions : 



" There is a correlation of structure and function as exhibited by 

 a progressive complexity of cell lamination of the visual cortex in 

 mammalia from the insectivora to primates. The more the animal 

 depends on vision as a directive faculty in its preservation the more 

 complex is the structure. 



i4 The transition of uniocular panoramic to perfect binocular 

 stereoscopic vision shows successive stages in the number of direct 

 fibres until, in the primates, there is semidecussation and, as far as 

 my observations go, this may be correlated with a progressive develop- 

 ment in the layer of higher associational pyramidal cells lying above 

 the layer of 'granules. 



" The progressive evolution of vision as a directive faculty is 

 simultaneous with a motor adaptation, especially related to the mode 

 of feeding and defence rather than to a particular species. 



" Carnivorous animals, especially cats, therefore, have their eyes set 

 forward, abundant direct fibres, and good binocular vision, to enable 

 them to seize their rapidly moving prey with their teeth or paw. 



" Better motor adaptation, as Sherrington has independently 

 suggested from his flicker observations, then is probably the essential 

 cause of the direct path of the op.tic fibres and binocular vision. 



" It is, however, in the primates that we have semidecussation 

 of the optic fibres, a macula lutea, eye movements in all directions 

 independent of head movements. Convergence and perfect binocular 

 stereoscopic vision associated with the hand, which, in the apes, be- 

 comes the principal executive agent in the procuring of food, defence, 

 and flight. Visual images are now always associated with impressions 

 of the exploring hand, and the ideas of form, substance, extension, 

 and qualities of objects are the complex of the visual and tactile 

 kinsesthetic images, and capable of endless variations. This we may 

 connect with the appearance in the zoological series of an occipital 

 lobe, a line of Gennari visible to the naked eye, a deep layer of 

 pyramids with a double layer of granules in the visuo-sensory striate 

 area. But even more important than this is the appearance of a 

 definite associational zone in which there is a much greater depth 

 of pyramidal cells, the third layer of which is characterised by very 

 large pyramids serving as higher complex association neurones between 

 the visual cortex and the auditorv and tactile motor areas. As we 



