650 



THE EYE 



in the outer nuclear layer and is continued as a fine filament, which, 

 having penetrated the external limiting membrane, extends as far as the 

 border line between the outer nuclear and outer reticular layers, at which 



a 



FIG. 550. A ROD AND A CONE 

 VISUAL CELL FROM THE FUN- 

 DUS OF THE HUMAN RE- 

 TINA, OUTSIDE THE MACULA 

 LUTEA. 



a, outer segment; 6, inner seg- 

 ment; c, rod- or cone-fiber; d, 

 nucleus; e, rod- or cone-foot; f, 

 ellipsoid; g, myoid (of cone); 

 h, external limiting mem- 

 brane. (Schafer, Greeff.) X 

 1000. 



FIG. 551. Two CONES FROM THE HUMAN 

 RETINA. 



A, from close to the ora serrata; B, from 

 near the margin of the forea centralis. The 

 fiber (f ) is cut short beyond the nucleus. Be- 

 tween the ora and the fovea cones of inter- 

 mediate lengths are found, forming a series 

 from A to B. In the central part of the 

 fovea, the cones are still longer than B, the 

 increase being due mainly to an elongation 

 of the outer segments (os) to about twice 

 the length in B. (Greeff.) X 1000. 



