252 



TWENTY-FOURTH LECTURE. 



but, notwithstanding the labors of H. Mueller and M. Schultze, 

 we are still exceedingly distant from a conclusion, as Schwal- 

 be's most recent studies show. 



The retina (Fig. 202) is invested externally by the simple 

 pigmented epithelial layer already familiar to us (p. 30). 



Then (1) we have the stratum of 

 rods and cones ; thereupon follows 

 the so-called external limiting mem- 

 brane, the membrana limitans ex- 

 terna (the transverse line between I 

 and 2). Next comes the external 

 granular la} T er (2), then the inter- 

 granular layer (3). Thereupon fol- 

 lows the inner granular layer (4), 

 then the molecular stratum (5). 

 Further inwards we meet with the 

 stratum of the ganglion cells (6), 

 thereupon the radial expansion of 

 the optic nerve fibres (7). The 

 termination is formed by the inter- 

 nal limiting membrane, the mem- 

 brana limitans interna (10). The 

 layer of rods and cones, as well as 

 the external granular layer, is called 

 by Schwalbe the neuro-epithelial 

 stratum, all the rest the cerebral 

 stratum. 



In the structure of this thin 

 and wonderfully complicated mem- 

 brane we must, however, distinguish two different elements, 

 connective tissue and nervous. 



Let us first take the former into account (Fig. 203, A), and 

 commence at the inner surface. 



The membrana limitans interna (/), an apparently hyaline, 

 o.oon mm. thick layer, deserves mention as the first connec- 

 tive-tissue boundary layer. In an inward direction (to- 

 wards the vitreous body), smoothly demarcated, it passes over 



Fig. 202. — The human retina in ver- 

 . tical section ; i, layer of the rods 

 cones, demarcated below by the mem- 

 brana limitans externa ; 2, the exter- 

 nal granular layer ; 3, intergranular 

 layer; 4, internal granular layer: 

 5, tine granular layer ; 6, layer of gan- 

 glion cells ; 7. expansion of the optic 

 nerve fibres ; 8, Mueller's supporting 

 fibres ; 9, their transformation into the 

 inner limiting. membrane ; 10, the mem- 

 brana limitans interna. 



