THE MACULA LUTEA 591 



The glia fibres then pass in a fairly straight course through the 

 inner reticular layer. In this portion numerous short, fine, lateral 

 offshoots from the main stem support the neurospongium of the 

 reticular layer. Continuing through the inner nuclear layer the 

 glia substance is somewhat thickened ; it send3 off fewer but coarser 

 lateral processes, and in the mid-region of this layer presents an 

 enlargement which is almost entirely occupied by the large ovoid 

 nucleus. 



The fibre cell, somewhat narrowed, may then be traced through 

 the outer reticular to the outer nuclear layer, where its processes 

 form a dense network about the nucleated segments of the rod and 

 cone elements. 



The terminal processes of the fibre cells become again flattened, 

 somewhat after the manner in which the internal limiting mem- 

 brane is formed, and are so closely approximated as to form an ex- 

 ternal limiting membrane, a distinctly membranous structure which 

 derives a reticular appearance from being pierced by each of the 

 innumerable rod and cone elements. 



From the outer surface of the expanded ends of the Miillerian 

 fibre cells which form the external limiting membrane, minute fibrils 

 are continued between the bases of the non-nucleated portions of the 

 rod and cone cells to form shallow sockets, the rod and cone sockets, 

 into which -the bacillary portions of these elements are fixed. 



THE MACULA LUTEA (linibus lutea, yellow spot], being ap- 

 parently the most highly developed portion of the retina, deserves 

 some special consideration. The macula is a circular elevation in 

 the center of which is a marked depression, the fovea centralis. 

 The elevation results from an increased thickness of all the retinal 

 layers, but 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 bacillary layer, within the 

 area of the macula, the cones are far more numerous than else- 

 where, especially when considered in relation to the rods, which are 

 greatly diminished. 



Toward the fovea centralis the inner layers of the retina become 

 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 elements are not found in this area ; the bacillary layer 

 consists entirely of cones. The much elongated nuclear portion of 

 the cones deviates in a slanting direction toward the margin of the 

 macula, and the cone nuclei are further removed from the external 



