THE GLOBE OF THE EYE. 



985 



2. External granular 



Fig. 507. 



between the external 



Fig. 508. 



for the latter, and equal in length to this segment for the rods. The inner seg- 

 ment is a small granular shaft for the rods, and an enlargement, the base of 

 which is towards the centre of the eye for the cones. The elements of this layer 

 quickly alter after death 



layer (2). — This is comprised 

 limitary and the intermedi- 

 ate membrane. It is formed 

 by the granules of the cones 

 and those of the rods — small 

 cells with an oval nucleus 

 {vision cells), furnished with 

 an external prolongation 

 that joins them to the base 

 of the cones and rods, and 

 an external varicose prolon- 

 gation which often enlarges 

 on arriving at the inter- 

 mediate layer. 



3. Intermediate lager 

 (3). — This is very thin, and 

 composed of flexuous fi- 

 brillte, which are connected 

 with the adjoining elements. 



4. Inner granular layer 

 (4). — In this we find cells, 

 the membrane of which is 

 in immediate contact with 

 the nucleus. These cells 

 have minute prolongments 

 analogous to those of the 

 external granular layer, 

 which connect them with 



the surrounding layers, 



5. Molecular layer (5). 

 layer (the grey vesicular) presents a granulous aspect ; 

 in its mass, the connective tissue forms a close mesh, 

 in the midst ot which are seen fine fibrillae passing in 

 every direction. 



6. Ganglionic layer (6). — This is composed of a single 

 stratum of ramifying nerve-cells, the prolongations of 

 which pass into the molecular layer, where they join the 

 filaments of the next layer. 



7. Layer of the optic-nerve fibres (7).— The fibres 



(ultimate fibrils) of the optic nerve, in passing through the sclerotic and choroid, 

 anastomose with each other, and arrange themselves in a cone shape, the apex 

 of which corresponds with the papilla conica ; at this point they suddenly spread 

 out in every direction, between the ganglionic layer and the internal limitary 

 membrane. 



To sum up, the retina comprises the following layers, reckoning from before 

 to behind : 1. Internal limitary membrane. 2. Layer of optic-nerve fibres. 3. 



VERTICAL SECTION OF RKTINA. 



I, Bacillar layer; 2, outer grau- 

 ular layer; 3, intermediate 

 fibrous layer; 4, inner granular 

 layer; 5, finely granular grey 

 layer; 6, layer of nerve-cells; 



7, layer of fibres of optic nerve; 



8, limitary membrane. 



-One of the thickest, this 



DIAGRAM OF THE STRUC- 

 TURE OF THE RETINA. 



p, Pigment -cell of the 

 retina connected with a 

 rod ; n, cone seated on 

 the raembrana limitans 

 externa, the inner seg- 

 ment containing a cone 

 ellipsoid, and a needle ; 

 inf, proper fibre con- 

 necting rod and cone 

 with one of the cells of 

 the membrana fenestra, 

 the cells of which are 

 in communication with 

 the membrana limitans 

 interna, mli, by means 

 of a thick radial fibre 

 with an oval nucleus 

 attached ; gg, multi- 

 polar ganglion of nerve- 

 elements ; op, optic 

 fibrilla; gri, supposed 

 connectionof the nucleus 

 with prolongation of a 

 ganglion-cell. 



