442 



ORGANS OF THE SENSES. 



tends to prove rather a part of the retina than of the choroid 

 tunic. 



The retina is much thinner in one part than in others; in 

 other words, the passage of the nerve filaments from within to 

 without is much shorter; they exhibit no enlargement, and 

 end directly in their terminal organ. This point, which is 



Fig. 120. Elements and structure of the retina.* 



tinged yellow, is known by the name of yellow spot (macula 

 luted), and is (Fig. 121) situated a little outside of the optic 

 papilla, or precisely at the posterior extremity of the antero- 

 posterior diameter of the globe of the eye. At this point, 

 the terminal organs are all represented by cones, while in 

 other parts the rods and cones are intermixed, the former 

 becoming more rare as we examine the anterior part of the 

 retina, that is, the part farthest from the yellow spot. At 

 this part of the retina (region of the ora serrata ; see p. 

 437, Fig. 118, 15), all elements of which partake of the 

 nature of nerves gradually disappear, their place being 

 occupied by connective tissue elements, which are also found, 



* A, Vertical section of the substance of the retina, hardened by chromic 

 acid. I, Membrane, called the membrana limitans, with the ascending support- 

 ing fibres (of Muller). f, Layer of filaments of the optic nerve. </ ? Layer of 

 the nerve cells, n, Gray layer, finally granular, crossed by radiating fibres. 

 A;, Interior (anterior) granular layer, t, Intergranular layer. A/, Exterior (pos- 

 terior) granular layer, s, Layer of the rods and cones. B and C, Detached 

 ii laments, enlarged. 



