COLUMNAR LAYER OF THE RETIXA. 



727 



1. The columnar layer (stratum bacillorum), consists of innumerable thin 

 rods, placed vertically side by side like palisades, and of other larger bodies, 

 more or less thickly interspersed amoog these, and named cones. These 



Fig. 476. 



Fig. 476. VERTICAL SECTION OP A SMALL PART OF 

 THE RETINA (after Kolliker). ^ 



A, entire section of a small part of the retina ; B, 

 two cones represented separately in their connection 

 with the fibres of Miiller and other structures ; C, 

 two rods represented separately iu their connection 

 with the granules, fibres of Miiller, and the nerve- 

 cells ; 1, columnar layer ; a, in A and C, the rods, 

 in B, the terminal part of the cone ; b, cones ; 2, 

 granular layer ; c, outer layer of nuclei (striated 

 corpuscles of Henle) ; d, inner layer of nuclei ; /, 

 internuclear layer ; 3, nervous layer ; g, fiue mole- 

 cular substance outside h, the nerve-cells ; &, nerve- 

 fibres ; I, membraua liinitans ; e, inner ends of the 

 fibres of Miiller resting on the limiting membrane. 



structures are glistening, soft, easily des- 

 troyed, and lose their characters quickly in 

 fluids. The rods are of uniform diameter, 

 and are abruptly truncated externally. The 

 cones are flask-shaped in the inner part of their 

 extent, and taper to a rod-like extremity ex- 

 ternally. Each cone rests on a pyriform cell 

 continuous with it, and forming the extremity 

 of a fibre of Miiller ; while the rods end 

 internally in pointed extremities ranging with 



these pyriform cells, and represented as formed by similar bodies (Kolliker); 

 but this continuity with Miillerian fibres is still disputed. The dilated 

 portions of the cones present granular contents, and a similar appearance is 

 described in the inner halves of the rods. At the outer ends the rods pro- 

 ject somewhat farther than the cones. When the outer surface of the 

 retina is viewed about midway between its centre and margin with a strong 

 enough magnifying power, a number of minute globular-looking bodies, the 

 ends of the rods, appear ; and between them, at a deeper level, other 



Fig. 477. 



Fig. 477. OUTER SURFACE OP THE COLUMNAR LAYER OP 

 TBE RETINA (from Kolliker). - 



a, part of the columnar layer within the macula lutea, 

 where only cones are present ; b, part near the macula, 

 where a single row of rods intervenes between the cones ; c, 

 from a part of the retina midway between the macula and 

 the ora serrata, showing a preponderance of the rods. 



transparent larger bodies, the swellings of the cones, 

 are seen, with a smaller circle within each the end 

 of its narrower part. Towards the margin the rods 

 become more numerous ; near the centre the cones 

 predominate ; and in the macula lutea the cones alone are seen. 



2. The external and internal nuclear divisions of the granular layer are 

 two collections of rounded and oval corpuscles, refracting light pretty strongly. 

 The corpuscles of the internal nuclear layer are small cells with large nuclei, 



