550 STUDIES IN ADVANCED PHYSIOLOGY. 



that each side of the brain controls corresponding halves 

 of the retina, so that the loss of the right optic tracts, for 

 instance, would result in blindness of the left halves of 

 both retinas. Of course if the optic nerve itself were cut 

 then the entire retina to which it went would become blind. 



10. The Microscopic Striicture of the Retina. In order 

 to understand the physiology of the eye it is not absolutely 

 necessary to go into the histological structure of very many 

 of its parts. An exception to this, however, is the retina, 

 which, as the seat of vision, has an exceedingly delicate 

 structure, by means of which the light may be perceived. 

 The microscope readily reveals ten distinct layers. These 

 are, beginning with the one next to the hyaloid membrane, 

 as follows: 



First, a thin transparent membrane called the internal 

 limiting membrane. 



Second, a nerve fiber layer continuous with the optic 

 nerve at one end and extending further into the retina at 

 the other. 



Third, the nerve cell layer, an ordinary ganglionic layer 

 with which the nerves of the second layer probably connect. 



Fourth, an inner molecular layer seen to consist of thin 

 sections of very small granules, which granules, however, 

 are probably systems of dendrons cut across. It seems prob- 

 able that this molecular layer is a layer in which the dend- 

 rons of consecutive neurons meet. This is succeeded by, 



Fifth, the inner nuclear layer, consisting of larger 

 granules, which are undoubtedly small nerve cells, so that 

 this layer may be looked upon as a second ganglionic layer. 

 Next to this is found, 



Sixth, the outer molecular layer, differing from the 

 inner molecular layer only in being much narrower. This 

 is succeeded by, 



Seventh, the outer nuclear layer similar in construction 

 to the inner nuclear layer and ganglionic in its function. 

 The outer nuclear layer is bordered by a very thin mem- 

 brane called, 



