198 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



LEFT RETINA 



RIGHT RETIW 



mesial surface of the brain, and this portion of the occipital lobe 

 should be regarded as the true cortical center for vision, the re- 

 mainder of the occipital cortex being perhaps the seat of visual 

 memories or associations. There seems to be much evidence 

 indeed that the immediate ending of the optic paths lies in this 

 region. Thus, Donaldson* found, upon examination of the brain 

 of Laura Bridgman, the blind deaf-mute, that the cuneus espe- 

 cially showed marked atrophy, and clinical cases of lesions of the 

 cuneus have been found to be associated with a marked degree of 

 hemiopia. So also Flechsig,f by means of the myelinization 

 method, finds that the optic fibers end chiefly along the margin 

 of the calcarine fissure. It has been assumed that the fibers 



from the fovea of the retina 

 end in this region, according 

 to some authors (Henschen) 

 along the anterior third of the 

 fissure, according to others 

 (Schmid and LaqueurJ) along 

 the posterior portion of the 

 fissure. Moreover, since uni- 

 lateral lesions of the occipital 

 lobe, however extensive, do 

 not cause complete blindness 

 of the foveal region, it has 

 been supposed that this im- 

 portant part of the retina is 

 bilaterally represented in the 

 cortex, as indicated in the ac- 

 companying diagram (Fig. 87) ; 

 so that complete foveal blind- 

 ness that is, blindness of the 

 centers of the visual fields can 



Fig. 87. Diagram showing the probable , nopnr whpn hnth OPpinitfll 



relati9ns between the parts of the retina and Only OCC T \V IM 



the visual area of the cortex. (From Schd- 1/VKoa aro ininrprl in tnp rpo*inn 



7r.) The bilateral representation of the looeS are H^UTC 



fovea is indicated by the course of the dotted o f ^he calcarine fissure. While 

 lines. . 



the general opinion seems to 



be that this last-named region is the main cortical ending of the 

 retinal fibers, especially of those arising from the foveal area, other 

 observers contend that the entire occipital cortex, lateral as well as 

 mesial surfaces, must be regarded as the cortical termination of the 

 visual paths, and that even the foveal portion of the retina is con- 

 nected with a wide area in this lobe. Monakow, for instance, ^points 



* Donaldson, "American Journal of Psychology," 1892, 4. 

 f Flechsig, "Localization der geistigen Vorgange," Leipzig, 

 j Schmid and Laqueur, "Virchow's Archiv," 158, 1900. 



1896. 



