STRUCTURE OF THE RETINA 



221 



optic nerve after it has passed through the coats of the eye (fig. 257). 

 At its entrance it forms a slight eminence (colliculus nervi optici). 

 The nerve -fibres lose their medullary sheath on reaching the retina. 

 The layer becomes gradually thinner in the anterior part of the retina. 



FIG. 257. SECTION THROUGH THE COATS OF THE EYEBALL AT THE POINT OF 



ENTRANCE OF THE OPTIC NERVE. (Toldt.) 



Ve, dural sheath ; Vm, arachnoidal sheath, and Vi, pia-matral sheath of the optic nerve, with 

 lymphatic spaces between them ; 0, 0, funiculi of the nerve ; L, lamina cribrosa ; A, central 

 artery ; S, sclerotic ; C'h, choroid ; R, retina. The small letters refer to the various parts of 

 the retina, 6 being the layer of rods and cones, and i that of nerve-fibres. 



The layer of nerve-cells, or ganglionic layer, is composed of large 

 nerve-cells somewhat like the cells of Purkinje of the cerebellum, and 

 having 011 the one side a fine axis -cylinder process prolonged into a 

 nerve-fibre, and on the other a thick branching process, the ramifica- 

 tions of which become lost in the next layer. 



The inner molecular layer is comparatively thick, and has an 

 appearance very like the neuroglia of the grey matter of the nerve- 

 centres. A few nuclei are scattered through it, and it is traversed by 

 the processes of the nerve-cells and of the inner granules, as well as by 

 the fibres of Miiller. 



The inner nuclear layer is mainly composed of bipolar cells con- 

 taining large nuclei (inner granules). The processes of these cells 

 extend on the one hand inwards through the inner molecular layer, 

 probably to join with nerve-fibres or with the processes of the gan- 

 glion-cells, whilst the other process is directed outwards, and is con- 

 nected with the extremity of a rod or cone fibre. Besides these bipolar 

 cells, there are other inner granules which are different in character, 

 being devoid of processes and resting on, or even embedded in, the 



