108 YETEKINAKY OT'HTHALMOLOGY. 



the fibers just mentioned with some molecular matter. 

 (7) The external gramdar layer. Composed of both, 

 iierve and connective tissue elements. Former consists 

 of bi-polair cells, from which offshoots pass out to the 

 rod and cone layer and inward to the internal granular 

 layer. (8) The external limiting mernbrane, foa'med by 

 the terminal extremities of Muller's fibers. (9) The 

 layer of rods and cones. The rods commence as fine 

 fibers in the outer molecular layer, pass through the 

 outer granular, and just beneath the external limit- 

 ing membrane begin to increase in size, forming the 

 rod granule, and some distance after passing through 

 this membrane they taper down into cylindrical-shaped 

 rods which extend outward to the pigment layer. The 

 cones also commence as a cone-shaped swelling in the 

 outer molecular layer, where they are in direct commu- 

 nication with tire fibers from the internal granular 

 layer. The cone fiber becomes thinner until, just un- 

 derneath the external limiting- membrane, it again 

 swells rapidly and there forms the cone itself, whicli 

 contains a large oval nucleus and nucleolus. The cones 

 are shorter and thicker than the rods, and are of 

 a bottle-shaped appearance. The rods and cones are 

 arranged perpendicularly to the plane of the retina, 

 and may be divided into an inner and outer part. The 

 inner is thickest and appears granulated ; the outer is 

 broken up into highly refracting lamellse, appearing 

 like superposed discs or piles of coins. (10) The pig- 



