SENSE OF SIGHT. 



551 



cells. In the macula lutea the cells are smaller, and lie in several 

 layers. The shape of these ganglion-cells is peculiar, resembling 

 somewhat those of Purkinje in the cerebellum. The portion 

 which is in contact with the nerve-fiber layer is rounded, and 

 from it is given off an axis-cylinder process which is continuous 

 with one of the axis-cylinders which make up the nerve-fiber 

 layer. From the opposite side of each cell is given off a thick 

 process which branches, the branches ending in arborizations at 

 different levels in the fourth or inner molecular layer. 



4. Inner Molecular Layer. This is called also inner granular 

 layer, by reason of its granular appearance, and also reticular layer. 

 It is relatively thick, and consists of a reticulum of nerve-fibers 

 with interspersed granules, of processes of the cells of the gan- 

 glionic layer, and of those of the inner nuclear layer. 



5. Inner Nuclear Layer. The characteristic elements of this 

 layer are bipolar nerve-cells in which are large nuclei ; these 

 cells are called inner granules. The process of each of these 

 cells which passes inward terminates in arborizations in the inner 

 molecular layer ; the process that passes outward terminates in a 

 similar manner in the outer molecular layer. There are two kinds 

 of these bipolar cells : (1) Rod-bipolars and (2) cone-bipolars. 

 The rod-bipolars are connected externally with the rods of the 

 retina, and internally with the rods of the ganglionic layer. The 

 cone-bipolars are connected with the cones of the retina exter- 

 nally, while internally they ramify in the middle of the inner 

 molecular layer. 



In addition to bipolar cells there are amacrine-celh, so called 

 because they lack long processes, although from some of them 

 axis-cylinder processes are given off which may extend into the 

 nerve-fiber layer. The bodies of these cells are often partly in 

 the inner molecular layer, and they are sometimes called spongio- 

 blasts of the inner molecular layer. From them are given off 

 branching processes or dendrons which pass into the inner molec- 

 ular layer. 



Horizontal cells of Cajal or spongioblasts of outer molecular 

 layer are cells in this layer which send processes into the outer 

 molecular layer. 



6. Outer Molecular Layer. This is a thin layer, and consists 

 of the arborizations of the inner nuclear layer, of the rod- and 

 cone-fibers, and of the horizontal cells of Cajal. Schafer states 

 that up to this point i. e., including the outer molecular layer 

 the retina may be regarded as composed of nervous elements, 

 but beyond it is to be considered as formed of modified epithe- 

 lium-cells. 



7. Outer Nuclear Layer. In this layer are found cells charac- 

 terized by transverse striations, passing off from which externally 

 are processes connected with the rods of the ninth layer, by reason 



