1196 THE FIBRES OF MULLER. [BOOK in. 



peculiar shaped bodies known as the radial fibres of Muller (Fig. 

 145). Each fibre is the outcome of the changes undergone by 

 what was at first a simple columnar epithelial cell. The changes 

 are in the main that the columnar form is elongated into that 

 of a more or less prismatic fibre, the edges of which become 

 variously branched, and that while the nucleus is retained the 

 cell-substance becomes converted into neurokeratin (see 563). 

 And indeed at the ora serrata the fibres of Muller may be seen 

 suddenly to lose their peculiar features and to pass into the 

 ordinary columnar cells which form ( 714) the pars ciliaris 

 retina3. 



At the inner limiting membrane, the fibre of Muller begins 

 with a broad expanded foot fused with the membrane ; indeed 

 the inner limiting membrane may be regarded as in reality formed 

 out of the coalesced broad more or less polygonal bases of the 

 fibres of Muller. From this broad base the fibre narrows to a thin 

 columnar body stretching radially outwards through the layer of 

 optic fibres and that of ganglionic cells. From the edges of the 

 body numerous fine processes extend in various directions, affording 

 support to the optic fibres which wind in and out between the 

 feet of, and to the ganglionic cells which are lodged in the spaces 

 between the bodies of these fibres of Muller. Stretching still 

 radially outwards the fibre as it passes through the inner 

 molecular layer gives off processes which either divide into or at 

 least are lost in the numerous neuroglial fibres forming part of 

 the fibrillar structure of that layer. In the inner nuclear layer 

 broader lateral processes become especially abundant, forming a 

 neurokeratinal basketwork in the spaces of which the nervous 

 elements of this layer are lodged ; and here the body of the 

 fibre bears the nucleus (Fig. 145 ri) of the fibre itself, a somewhat 

 elongated oval nucleus placed vertically. At the level of the outer 

 molecular layer the body of the fibre seems to end, its processes 

 contributing to form that layer in some such manner as in the 

 inner molecular layer, but in reality it breaks up into a basket- 

 work or sponge work of delicate neuro-keratinal shreds, supporting 

 the nervous structures of the outer nuclear layer, and terminating 

 at the outer limiting membrane or, possibly, even passing beyond 

 it. 



Each fibre of Muller may be regarded as a brace or tie between 

 the inner and the outer limiting membrane, its nucleus appearing 

 among the nuclei of the inner nuclear layer, and its numerous 

 processes on the one hand contributing to form the inner and 

 outer molecular layer and on the other hand affording throughout 

 the thickness of the retina a support for the nervous elements. 



Besides these conspicuous fibres of Muller, which we may 

 regard as large neuroglial elements, small, more ordinary neuro- 

 glial cells are also present in the various layers, especially perhaps 

 in the outer molecular layer and in the layers of optic fibres and 



