590 



THE EYE 



with a sharp curve almost at right angles to their former course. 

 At this point also they gradually acquire a medullary sheath, and, 

 uniting into many bundles, penetrate the numerous openings of the 



laminae cribrosae of the sclerotic and 

 choroid coats to form the optic nerve. 



THE SUPPORTING TISSUES OF 

 THE RETINA. These consist of a 

 gliaform reticulum distributed through- 

 out the cerebral portion of the retina, 

 and of a special supporting tissue, Miil- 

 ler's fibres, which may also be regarded 

 as glia tissue, though they are common 

 to both the neural and epithelial por- 

 tions. 



The fibres of Mtiller comprise numer- 

 ous large glia cells whose processes be- 

 gin with an expanded base at the inner 

 surface of the nerve fibre layer, and can 

 be traced all the way through the retina 

 to the membrana limitans externa, which 

 is likewise formed by the terminal ex- 

 pansions of these cells. The nucleus 

 of the fibre cell lies in the mid-region of 

 the inner nuclear layer. 



The expanded and flattened bases or 

 inner extremities of these glia cells are 

 so closely approximated to one another 

 as to form a complete investment for 

 the inner surface of the retina, which is 

 known as the internal limiting mem- 

 brane (membrana limitans intern a) and 



3. 



I. 



m.l.i* 



FIG. 434. A FIBRE CELL OK 



MttLLEK FKOM THE DOG'S 

 KETINA. 



1, nerve fibre layer ; 2, gan- 

 glion cell layer ; S, inner reticular is f requ ently classed as the innermost 

 layer ; 4, inner nuclear layer ; 5, * , t ._ 



outer reticukr layer; e, outer layer of the retina. Under low magnifi- 



nuclear layer; a, a process ex- cation it appears as a continuous mem- 

 tending into the inner reticular b but under h j her rg it ig 

 layer; 6, nucleus of the cell; 



readily resolved into the broad, conical, 

 basal expansions of which it consists. 

 From these initial expansions the glia 

 cells may be traced outward through the 



nerve fibre and ganglion cell layers by means of the numerous 



coarse processes or glia fibres. 



m. L e., external limiting mem- 

 brane ; m. I. i., internal limiting 

 membrane. Golgi's stain. High- 

 ly magnified. (After Cajal.) 



