THE EYE. 



423 



cells situated in the outer region of this layer and 

 expanding in a horizontal direction. (6) The outer 

 molecular layer, like the inner molecular, is a net- 

 work of fibrils, processes from all the ganglion cells 

 of the retina and also neuroglia elements. The ex- 

 ternal portion of this molecular layer is not so densely 

 packed with fibrils and has been called Henle's fiber 

 layer. (7) The outer nuclear layer is composed of 

 many compact rows of nuclei and is the most con- 

 spicuous layer in stained sections of the retina. The 

 cell bodies enclosing most of these nuclei are the 

 visual units of the eye and are called rod-visual and 

 cone-visual cells, as the rods and cones are merely 

 processes of these cells. The cells are elongated units 

 whose long axis is placed radial to the eye, and whose 

 multiple processes enter the outer molecular layer 

 as already mentioned. The cone-visual cells are 

 least numerous and their nuclei are placed at regular 

 intervals in the outer portion of the layer. Their 

 nuclei are somewhat larger than the nuclei of the 

 other cells. Rod-like neuroglia elements give sup- 

 port to the visual cells. (8) The external limiting 

 membrane invests the outer nuclear layer. It is a 

 thin, transparent, homogeneous membrane, derived 

 from the neuroglia tissue, and forming a dividing line 

 between the rods and cones and the outer nuclear 

 layer. (9) The rods and cones are processes from the 

 visual cells whose nuclei form the bulk of the outer 

 nuclear layer. The rods are 40 /> to 50 n in length, 

 and consist of two segments, the outer being doubly 

 refractive to light, and may be separated into numer- 

 ous transverse discs by the action of certain reagents. 



