108 VETERINAPvY OPHTHALMOLOGY. 



the fibers just mentioned with some molecular matter. 

 (7) The external granular layer. Composed of both 

 nerve and connective tissue elements. Former consists 

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

 rod and cone layer and inward to the internal granular 

 layer, (8) The external limiting membrane^ formed by 

 the terminal extremities of Miiller's fibers. (9) Tlie 

 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 the 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, which 

 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 lamellae, appearing 

 like superposed discs or piles of coins. (10) The 2>ig- 



