218 



SENSE OF SIGHT. 



with analogy. On its inner surface it is 

 in contact with the membrane of the vitre- 

 ous humour; but they are not adherent. 

 Anteriorly, it terminates near the ante- 

 rior extremity of the choroid, forming a 

 kind of ring, from which an extremely 

 delicate lamina is given off. This is re- 

 flected upon the ciliary processes; dips into 

 the intervals separating them, and, accord- 

 ing to some anatomists, passes forward 

 as far as the crystalline. Modern ob- 

 ^ servers Messrs. B. C. R. Langenbeck, 



Part of the Retina of a Frog seen m >->, . , TT n -r\ TT 



from the outer surface? Treviranus, Gottsche, Volkmann, E. H. 

 Magnified 300 times. (Treviranus.) Weber, Michaelis, and others, have ex- 

 amined minutely into the anatomy of the 



retina, and have shown that it consists of several layers : Langenbeck 

 says three; Michaelis, four. The outer layer of the true retina is con- 

 sidered to be formed by the optic nerve, which, at its entrance into the 

 eye, divides into numerous small fasciculi of ultimate fibrils, that 

 spread themselves out, and inosculate with each other by an inter- 

 Fig. 91. 



Vertical Section of the Human Retina and Hyaloid Membrane. 



h. Hyaloid membrane, h' . Nuclei on its inner surface, c. Layer of transparent cells, connecting 

 the hyaloid and retina, c'. Separate cell enlarged by imbibition of water, n. Gray nervous layer, 

 with its capillaries. 1. Its fibrous lamina. 2. Its vesicular lamina. 1'. Shred of fibrous lamina de- 

 tached. 2'. Vesicle and nucleus detached, g. Granular layer. 3. Light lamina frequently seen, g' . 

 Detached nucleated particle of the granular layer, m. Jacob's membrane, m 1 . Appearance of its par- 

 ticles, when detached, in" . Its outer surface. Magnified 320 diameters. 



change of fibrils, so as to form a net-like plexus. From this plexus, the 

 fibres of which lie in the plane of the surface of the vitreous humour, 

 a very large number of fibrils arises in a direction perpendicular to 

 the surface, so as to be all directed towards the centre of the eye. 

 These pass through a delicate layer of areolar tissue, containing a 

 minute plexus of bloodvessels, and from this every fibril receives a 

 sheath, which envelopes its extremity, and thus forms a minute papilla. 

 The surface of the retina, in contact with the vitreous humour, is 

 wholly composed of these papillae, which are closely set together. Dr. 



