NERVOUS CONSTITUENTS OF THE RETINA. 231 



of the cells it is scarcely possible to see whether any processes 

 are given off at all, either on account of their being so closely 

 compressed against one another, or because they are covered 

 by the fibres of the optic layer. The results of the examination 

 of teazed-out preparations and sections, so far as they have 

 been at present used for the study of the ganglion cells, show 

 that the number of these processes, like those of the ganglion 

 cells of the central organs of the nervous system, varies con- 

 siderably. Cells with many processes have been most com- 

 monly depicted, but many cells also occur with only two 

 processes, as at the yellow spot (fig. 346, J5), and unipolar cells 

 have also been described. 



In 1850, Corti* pointed out the similarity of the appearance 

 of some of the ganglion-cell processes to fibres of the optic 

 nerve layer, and, relying essentially upon the above-described 

 fusiform varicosities, which occur in both, came to the con- 

 clusion that the optic-nerve fibres were directly continuous 

 with the ganglion cells. Attention has been called to the 

 agreement in character of the ganglion-cell processes with 

 the nerve fibres of the retina, by Remak, Hannover, H. Miiller, 

 Kolliker, and many others. The cells lie in immediate contact 

 with the layer of nerve fibres, and are, in fact, interposed be- 

 tween the fasciculi of the latter, whilst their processes may be 

 followed for considerable distances, and agree in all points with 

 the fibres of the optic-nerve layer ; under these circumstances 

 it is impossible to doubt that the fibres are directly continuous 

 with the cells. Another question is, whether all optic-nerve 

 fibres are connected with ganglion cells before they reach the 

 external layers of the retina. It is possible that a part of 

 those differences in the function of the several optic-nerve 

 fibres which we are compelled to admit on physiological 

 grounds, stand in direct relation to the presence or absence of 

 a connection between the fibres and the ganglion cells. Upon 

 this point, however, no positive statement can at present be 

 made. 



According to a method suggested by Manz,f the optic layer 



* Mliller's Archiv, 1850, p. 273, Taf . vi. 



t Zeitscfirift fur rationelle Medizin, Band xxviii. , p. 231, 1866. 



