~,g THE RETINA. 



1 The hexagonal pigment-cells already described. 2. The layer of rods and cones (*) or 

 J^^SSStf sSSalbe [bacillary layer, or the visual cells, ovvxmalepitMiumoi kuhne] 

 ^520) Th.se lie externally next the choroid, but they are absent at the entrance of the 

 optic ne ve. Then follows the external limiting membrane , (Le which is per orated by the 

 Sues of the rods and cones. 3. The external nuclear layer (au.K) ; this and all the succeed- 

 in^lavr; arc called brain layers" by Schwalbe. 4. The external granular (au.gr), or inter- 

 Sfitfkm which is perforated by the fibres which proceed inwards from the nuclei of 3 to 

 n < fa 5 L nuclei of the internal nuclear layer (inK). The nuclei of this layer, which are 

 connected by fibres with the rods and cones, are marked by transverse lines m the macula lutea 



(Krause, Dcnissenko). 6. The finely granular internal 



granular layer (in.ijr), through which the fibres proceeding 

 from the inner nuclear layer cannot be traced. It would 

 seem as if these fibres break up into the finest fibrils, into 

 which also the branched processes of the ganglionic cells 



Fig. 



MA 



Fig. 519. Fig. 520. 



519. Vertical section of human retina, a, rods and cones ; b, ext, and,/, int. limit, 

 memb. ; e, ext., and/, int. nucl. layers ; e, ext, and g, int. gran, layers ; h, blood-vessel 

 and nerve-cells; i, nerve-fibres. Fig. 520. Layers of the retina. Pi, hexagonal pigment- 

 cells ; St, rods and cones ; Le, ext. limiting membrane ; au.K, ext. nuclear layer ; du.gr, 

 ext granular layer ; inK, int. nuclear ; in.gr, int. granular ; Ggl, ganglionic nerve-cells ; 

 o, fibres of optic nerve ; Li, int. limit, membrane ; Ek, fibres of Miiller ; K, nuclei ; Sy, 

 spaces for the nervous elements. 

 of 7, the ganglionic layer, extend. According to v. Vintschgau, the processes of the gan- 

 glionic cells are connected with the fibres. 8. The next, or fibrous layer, consists of the fibres 

 of the optic nerve (o), and most internally is the internal limiting membrane (Li). Accord- 

 ing to W. Krause, there are 400,000 broad, and as many narrow, optic fibres, so that for every 

 fibre there are 7 cones, about 100 rods, and 7 pigment-cells. The optic fibres are absent from 

 the macula lutea, where, however, there are numerous ganglionic cells. Between the two 

 homogeneous limiting membranes (Le and Li) lies the connective-tissue substance of the 

 retina. It contains the perforating fibres, or Muller's fibres, which run in a radiate manner 

 between the two membranes, and hold the various layers of the retina together. They begin 

 by a wing-shaped expansion at the internal limiting membrane (Ek), and in their course out- 

 wards contain nuclei (k). They are absent at the yellow spot. The supporting tissue forms a 



