EYE 



447 



In addition to the nervous elements, the retina contains blood vessels 

 and a supporting framework of neuroglia cells. The largest vessels are 

 toward the fiber layer (Fig. 453), in thich they travel to and from the cen- 

 tral vessels in the papilla. The neuroglia framework consists chiefly of 

 radial (or Miiller's) fibers, which are elongated cells extending from the 

 internal to the external limiting membrane. Beyond this membrane they 

 send short processes between the rods and cones, forming "fiber baskets" 

 (Fig. 455). The radial fibers are not isolated cells but are parts of a 

 general syncytium, being connected by a network of processes which pene- 

 trate all the layers of the retina (Fig. 454). The external limiting mem- 

 brane, through which the rods and cones pass, is formed by the coa- 



- Fiber basket. 



Nucleated part of the 



fiber. 



.. Basal pyramid. 



Precipitate. 



FIG. 455. GOLGI PREPARATION OF RADIAL FIBERS IN A THICK SECTION OF THE HUMAN RETINA. 

 The fine processes of the fibers in the outer nuclear layer appear as a compact mass. X 360. 



lescence of these processes, and the internal limiting membrane is made up 

 of the closely adjacent basal expansions of the radial fibers. The nuclei 

 of the fibers are found in the inner nuclear layer. In addition to the radial 

 fibers there are neuroglia cells with horizontal or tangential branches 

 (Fig. 454, "oo")- As in the central nervous system, some of the stellate 

 groups of fibers do not contain nuclei. 



Two modifications of the retina require special description, namely, 

 the fovea centralis, which is the region of most acute vision, and the pars 

 ciliaris, which is the rudimentary peripheral portion. 



Macula lutea and fovea centralis. When vision is centered upon a 

 particular object, the eyes are so directed that the image of the object falls 

 upon the macula lutea, or yellow spot of the retina, within which there is 

 a depression, the fovea centralis. The macula sends straight slender 



