234 THE RETINA, BY MAX SCHULTZE. 



on the basis of the preceding observations, and with the ex- 

 ception of those at the yellow spot. The internal granulated 

 layer interrupts our knowledge of the course of the nerve fibres, 

 which again become visible in the outer layers of the retina. The 

 thickness of the internal granulated layer in Man varies, accord- 

 ing to H. Miiller, between 03 and O04 of a millimeter. 



The cause of the appearance, in sections of the retina of many 

 animals, of dark strise, which run parallel to the surface, and 

 give indications of a lamination of the granulated substance 

 concentric with the tunics of the eye, has not as yet been satis- 

 factorily ascertained. G. Wagner* states that he has counted 

 eight such layers. The spongy connective tissue, as my in- 

 vestigations on the retinae of Sharks show, takes some share in 

 its formation, the meshes being somewhat smaller in the darker 

 bands.f 



The layer of internal granules which succeeds externally to 

 the granulated layer contains, as VintschgauJ and H. Muller 

 were already aware, two distinct kinds of cellular elements 

 which are connected with two different kinds of fibres that 

 pursue an essentially radial course. Besides the radial sup- 

 porting fibres, which occupy a considerable space in this layer, 

 and intercommunicate by numerous bridges and intercalated 

 plexuses, there are numerous similarly radiating nerve fibres, the 

 course of which only in some few instances differs from that of 

 the supporting fibres, in being directed obliquely towards the 

 surface of the retina. These exactly resemble the fibres of 

 the optic layer, and are distinguished by their fusiform varicosi- 

 ties and smooth surface from the rough finely dentated sup- 

 porting fibres. In both kinds of fibres nucleated spots are 

 imbedded, and these represent the so-called internal granules. 



* Sitzungsberichte der Marburger naturforsch. Gesellschaft,Juli, 1868, No. 

 5, p. 47. 



t De retina structura penitiori, fig. 5. 



* Hicer che sulla structura microgr. della retina dell' uomo, degli animali 

 vertebrati e di Ceptialopodi. Sitzwigsberichte der Wiener Acad. d. Wissen- 

 schaften, Band xi., 1853, figs. 1, 5, 6, 9. 



In Falco buteo. Max Schultze, Archiv fur Microscopische Anatomie, 

 Band ii., p. 262. And, according to Hulke, in the yellow spot of Man, 

 Philosoph. Transact., 1868, p. 112. 



