THE GLOBE OF THE EYE. 



985 



External granular 

 Fig. 507. 



Fig. 508. 



for the latter, and equal in length to this segment for the rods. The innm- mj- 

 inent 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 {'>). — This is compri.sed between the external 

 liiiiitary and tlie intermedi- 

 ate membrane. It is formed 

 by the yranales of the roiie.s 

 and those of the rods — small 

 cells with an oval nucleus 

 (rifiion 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 layer 

 (3). — This is very thin, and 

 composed of flexuous fi- 

 brilltE, which are connected 

 with the adjoining elements, 



4. Inner yramdar 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 



tlie surrounding layers. 



5. Molecular layer (5). — One of the thickest, this 

 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 fibrillse passing in 

 every direction. 



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

 stratum of ramifying nerve-cells, the prolongations of 

 which p.iss 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. 



VERTlCAr, SECTION (JF RKTIN'A. 



1. Bacillar layer; 2, outer ginn- 

 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. 



DIAGRAM OF THE STRUC- 

 TU[{E OF THE RETINA. 



p, Pigment -cell of the 

 retina connected witli a 

 rod ; n, cone seated on 

 the membrana limitans 

 externa, the inner seg- 

 ment containing a cone 

 ellipsoid, and a needle; 

 mf, 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 

 connection of the nucleus 

 with prolongation of a 

 ganglion-cell. 



