900 



THE ORGANS OF SENSE. 



It is made up of a dense reticulum of minute fibrils, intermingled with the fine 

 processes of the ganglion-cells and also processes derived from certain cells 

 contained in the next layer, immediately to be described. No direct connection 

 between these sets of processes has yet been demonstrated, but it is considered 

 probable that they do communicate, and that there is therefore a direct connection 

 between the ganglion-cells of the vesicular layer and the nuclear cells of the inner 

 nuclear layer. Within the reticulum formed by these fibrils minute clear granules, 

 of unknown nature, are imbedded. 



5. The inner nuclear layer is made up of nuclear bodies, of which there are 



FIGS. 533, 534. Vertical sections of the human retina. Fig. 533, half an inch from the entrance of the optic 

 nerve. Fig. 534, close to the latter. 1. Layer of rods and cones (columnar layer), bounded underneath by the 

 membrana limitans externa. 2. External nuclear layer. 3. Outer molecular layer. 4. Internal nuclear layer. 

 f>. Inner molecular layer. 6. Layer of the ganglion-cells. 7. Expansion of optic fibres. 8. Sustentacular fibres 

 of Miiller. 9. Their a'ttachment'to the membrana limitans interna. 



three different kinds : (1) A large number of oval nuclei, which are commonly 

 regarded as bipolar nerve-cells, and are much more numerous than either of the 

 other kind. They consist of a large oval nuclear body placed vertically to the 

 surface, containing a distinct nucleolus : they are surrounded by a small amount 

 of protoplasm, which is prolonged into two processes : one of these passes inward 

 into the inner molecular layer, is varicose in appearance, and, as stated above, is 

 believed to be continuous with the processes of the ganglion-cells. The other 

 process passes outward into the outer molecular layer, and there bifurcates. 

 According to some observers, the divisions thus formed communicate with the rod- 

 and cone-fibres (Merkel). (2) At the innermost part of this inner nuclear layer 

 is a stratum of cells which are not branched. (3) Some few cells are also found 

 in this layer connected with the fibres of Miiller, and will be described with those 

 structures. 



6. The outer molecular layer is much thinner than the inner molecular layer, 

 but, like it, consists of a dense network of minute fibrils, and presents the same 

 granular appearance. It differs, however, from the inner molecular layer in con- 

 taining branched stellate cells, the processes of which are extremely fine and 

 exhibit varicosities like nerve-fibrils. They are therefore considered by Schultze 

 to be ganglion-cells. 



1. The Outer Nuclear Layer. Like the inner nuclear layer, this layer contains 

 several strata of clear oval nuclear bodies ; they are of two kinds, and, on account 

 of their being respectively connected with the rods and cones of Jacob's membrane. 



