Ill TIIK NERVOUS S^STKM AM) ITS CONSERVATION 



arc significant chiefly as they forward impulses to other 

 place-. As Loch has >aid. this is a dynamic rather than a 

 static form of localization. As this is true of the seii>ory 

 impulses from the body at large, so it is probably true for 

 the more highly developed sense organ>. such as the eye 

 and the ear. 



In the brain of man, as in that of the monkey, the visual 

 impulses or, rather, the impulses of visual origin are 

 projected to the hinder part of the cortex and, chiefly, to 

 the area called the cuneus. This is a distinctly marked 

 triangle set off by fissures upon the surface of the occipital 

 lobe which confronts the corresponding area of the opposite 

 >ide. A- the relation between the cerebrum and the skele- 

 tal muscles is so largely a crossed or cont ralateral one, the 

 inference might easily be drawn that the impulses from 

 the right eye would be found to arrive in the cortex of the 

 left side, but in the human organism this is not so. The 

 relationship is less simple. Approximately half of each 

 eye has efficient connections with the cerebral cortex on 

 the same side. An able teacher has likened the situation 

 to that of a driver with a pair of horses. His right hand 

 holds the reins which connect with the right side of both 

 the bits; his left hand is joined through the reins with the 

 left side of both. Carrying this comparison over to the 

 visual apparatus, it reads like this: the right occipital 

 cortex is functionally related with the right halves of 

 both the retime: the left cortex, with the left halves. 



The general statement just made requires a qualifica- 

 tion in view of a very interesting fact. There is in the 

 center of each retina a restricted region, the fovea, which 

 ha- superior visual possibilities, (When we speak of fix- 

 ing the eye on an object we mean fixing tin 1 image of the 

 object upon the fovea.) This part of the retina is believed 

 to have a double representation on the cortex both 

 eyes projecting impulses to both sides of the brain. 

 Thu>. no injury confined to one side of the brain can be 

 expected to destroy the use of either fovea. It can blot 

 out nearly, but not quite, half of the field of vision. The 



