THE ETE. 



825 



Fig. 388. 



Irana Jacobi (bacillary or columnar layer). It is situated between the inner 

 face of the choroid and the external limitary membr.me. 



Eods and cones, regularly mixed, make up its structure. Each of these 

 comprises two portions or segments (separated by a bright transverse line). 

 The outer segment (or shaft) is brilliant and 

 refractive, and consists of a small stalk termi- 

 nating in a point for the cones ; with a shorter 

 stalk than the inner segment for the latter, 

 and equal in length to this segment for the 

 rods. The inner segment .is a small granular 

 shaft for the rods, and an enlargement whose 

 base is towards the centre of the eye for the 

 cones. The elements of this layer quickly 

 alter after death. 



2. External granular layer (2). This is 

 comprised between the external limitary and 

 the intermediate membrane. It is formed by 

 the granulations of the cones and those of the 

 rods: small oval nucleated cells, furnished 

 with an external prolongation that joins them 

 to the base of the cones and rods, and an ex- 

 ternal varicose prolongation which often en- 

 larges on arriving at the intermediate layer. 



3. Intermediate layer (3). This is very 

 thin, and composed of flexuous fibrillte, which 

 are connected with the adjoining elements. 



4. Inner granular layer (4). In this we 

 find cells whose membrane is in contact with 

 the nucleus ; these cells have minute prolong- 

 ments analogous to those of the external 

 granular layer, and which connects them with 

 the 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 of which are seen fine fibrillse passing 

 in every direction. 



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

 ramified nerve-cells, whose prolongations pass into the molecular layer, 

 where they join the filaments of the next layer. 



7. Layer of 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, whose apex corresponds 

 to the papilla conica ; at this point they suddenly spread out in every 

 direction, between the ganglionic layer and the 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 ; 8, Layer of nerve-cells ; 4, Molecular layer ; 5, Inner granular 

 layer ; 6, Intermediate granule layer ; 7, Outer granular layer ; 8, Outer 

 limitary membrane ; 9, Columnar layer ; 10, Pigmentary layer of the 

 choroid, if this be attached to the retina, as Schultze proposes. 



It is to be remarked, that at the ora serrata all the nerve elements of the 

 retina disappear, and the membrane, reduced to its connective tissue, is 



VERTICAL SECTION OF RETINA. 



L, Bacillar layer ; 2, Outer granu- 

 lar 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, Limi- 

 tary membrane. 



