THE EYE 





cular elevation about 2 mm. in 

 diameter, in the center of which 

 is a marked depression, the fovea 

 centralis. It is yellow in color, 

 due to the presence of a pigment. 

 The elevation results from an in- 

 creased thickness of all the ret- 

 inal layers, hut especially of the 

 ganglion cell layer, which in this 

 portion of the retina is five or six 

 cells deep. The reticular layers 

 are also much thickened in this 

 area. In the hacillary layer, 

 within the area of the macula, 

 the cones are far more numerous 

 than elsewhere, especially when 

 considered in relation to the rods, 

 which are greatly diminished 

 peripherally and absent centrally. 

 The cones of the macula are al- 

 most twice as long as those of 

 the equatorial region of the re- 

 tina, the increased length being 

 due to elongation both of the in- 

 ternal and external segments, 

 but mainly the latter; they are 

 also somewhat more slender, and 

 their nuclei may be placed some 

 distance beyond the external lim- 

 iting membrane. 



Toward the fovea centralis 

 the inner layers of the retina be- 

 come very much thinned, until 

 at its center the nerve tissues are 

 merely represented by scattered 

 cells of the inner nuclear and 

 ganglion cell layers. Rod ele- 

 ments are not found in this area ; 

 the bacillary layer consists en- 

 tirely of elongated, slender cones. 



