176 OEGAJTS OF SENSE. 



sion of a light yellowish color the yellow spot of 

 Scemmering. As we trace it forwards, the retina grows 

 thinner, and its anterior border corresponds with the 

 outer circumference of the iris ; its nervous matter, 

 however, can be traced no farther than the com- 

 mencement of the ciliary processes, where it ter- 

 minates abruptly, by a serrated margin (or a serrata). 



The researches of H. Muller* demonstrate the 

 structure of the retina to be as follows : 



Its outer layer is made up of little " club-shaped 

 rods" arranged closely side by side so as to form an 

 uninterrupted lamina the membrana Jacolri. Their 

 direction is perpendicular to the surface of the retina, 

 and their shape, as their name indicates, is cylindri- 

 cal; but some of them enlarge at their outer extremi- 

 ties, so as to assume a conical form. These latter are 

 fewer in number than the club-shaped bodies first 

 mentioned, and are quite uniform in their distribu- 

 tion, with this exception, that they alone constitute 

 the whole thickness of Jacob's membrane where it 

 passes over the yellow spot of Soemmering. The 

 internal extremities of these club-shaped bodies taper 

 off, and each one of them, becomes continuous with a 

 fibre (fibre of Muller), which traverses the whole 

 thickness of the retina. In its course this fibre pre- 

 sents three distinct enlargements : the first is situated 

 at its outer extremity, just where it is joined by the 

 corresponding club-shaped body; the second at its 

 middle, and the third at its internal extremity. The 

 first corresponds to the external granular layer, which 



* Professor, or Lecturer, on Anatomy in the University of "Wurz- 

 burg, Bavaria. (Ed.) 



