NERVOUS CONSTITUENTS OF THE RETINA. 233 



for short distances, when they appear as extremely delicate 

 and very tortuous fibres, beset with distinct fusiform varicosities, 

 but otherwise smooth. The thicker and branched ganglion-cell 

 processes which dip into this layer, or belong to it from their 

 first origin from the cells, can be still more distinctly followed, 

 though little is known in respect to their mode of termination. 

 Some are continuous with immeasurably fine fibrils, which, 

 after a circuitous path, at length reach the outer layers of the 

 retina, whilst others, especially at the yellow spot, enter the 

 inner granule layer in the form of thick fibres. Such state- 

 ments have been made, amongst others, by H. Muller * and 

 K6lliker,-f- Gerlach,! Manz, and Merkel.|| The macula lutea, 

 on account of its less resistant connective tissue, appears 

 to be the part of the human retina best adapted to follow to 

 their termination the nerve fibres running in the granulated 

 layer. But inasmuch as the ganglion cells are here almost all 

 bipolar, whilst they are elsewhere multipolar, it becomes a 

 question whether great differences do not also exist in regard 

 to the course pursued by these processes. Speaking generally, 

 the same differences of opinion are held respecting the nature 

 of this granulated layer as of the grey granulated substance of 

 the cortex of the cerebrum.^I In particular, it is doubtful 

 whether, besides the fine and the very finest nerve fibres and 

 the plexuses of the connective substance, a certain number of 

 minute granules of unknown nature are not also present, as 

 appears to be the case, or whether the nerve fibrils and spongy 

 connective substance give rise by their peculiar disposition to 

 the finely granular appearance. 



In regard to the course and ultimate destiny of the processes 

 of the ganglion cells and the fine nerve fibres of this layer, we 

 must admit the impossibility of giving any positive statement 



* Zeitschrift fur wiss. Zoologie, Band viii. , p. 61. 



t Icones Physiologicce, Taf. xix., fig. 12. X. 



I Gewebelehre, 2nd edition, p. 498; fig. 220. 



Zeitschrift fur rationelle Medizin, Band xxviii., p. 237. 



j| Macula lutea, p. 11, fig. 9. 



IT See inter aliosH. Miiller, Zeits. fur ivissenschaft. Zoologie, Band viii., 

 p. 115 ; and Henle and Merkel, Zeitschrift fur rat. Med., Band xxxiv. 

 p. 49, 1869. 



