654 THE EYE 



roglia element, of the retina, and which extend from the extreme inner 

 surface outward to the external limiting membrane. It will therefore 

 be more convenient to defer further description of this membrane until 

 the remaining layers have been described, and the Miillerian fibers can 

 be considered in their entirety. 



4. The outer nuclear layer (outer granular layer) consists, for 

 the most part, of the nucleated portions of the rod and cone elements. 

 The outermost zone of this layer contains only cone nuclei; the inner 

 portion, comprising about three-fourths of its thickness, contains only rod 

 nuclei. The former, with occasional exceptions (Stohr), are situated in 

 only one relatively narrow plane ; the latter are distributed at various 

 levels, though they occur more abundantly in the mid-region of the 

 nuclear layer. In addition to portions of Miiller's fibers which serve for 

 the support of the nucleated elements, this layer contains the terminal 

 filaments of the distal processes of some of the small bipolar nerve cells 

 of the inner nuclear layer. 



5. The fiber layer of Henle is formed by that portion of the cone 

 fibers which is internal to the layer of rod nuclei. It is a thin layer and' 

 only acquires importance in the neighborhood of the macula lutea, where 

 the cones are most abundant. In this portion of the retina it is easily 

 distinguished from the outer reticular layer by the somewhat radial 

 disposition of its fibers, the fibers of the reticular layer having an irregu- 

 larly meridional direction. 



6. The outer reticular layer (outer molecular layer; outer plexi- 

 form layer) presents a dense tangle of neural tissues consisting of sup- 

 porting neuroglia fibers and interlacing processes from the horizontal 

 and bipolar nerve cells of the inner nuclear layer. Terminal fibrils from 

 this network intermingle in the fiber layer of Henle with terminal fibrils 

 from the cone feet; more externally they are in intimate relation with 

 the end knobs of the rod fibers. This arrangement permits the transmis- 

 sion of stimuli from the neuro-epithelium to the retinal ganglion. 



7. The inner nuclear layer (inner granular layer, ganglion retina, 

 outer ganglionic layer) contains a mass of nerve cells, together with the 

 nucleated portion of the sustentacular fiber cells of Miiller. The nerve 

 cells may be described as corresponding to one of three types, which, 

 from the plane in which they are distributed may be termed the outer, 

 middle, and inner. 



THE OUTER NERVE CELLS. The outer nerve cells (horizontal cells, 

 basal cells) possess pyramidal, stellate, or flattened cell bodies whose 

 dendrons are distributed to the horizontal plexus of the outer reticular 



