SENSE AREAS AND ASSOCIATION AREAS. 



209 



ate ending of the optic paths Res in this region. Thus, Donald- 

 son* found, upon examination of the brain of Laura Bridgman, 

 the bhnd deaf-mute, that the cuneus especially showed marked 

 atrophy, and Flechsig, f by means of the myelinization method, 

 arrived at the conclusion that the optic fibers end chiefly along 

 the margin of the calcarine fissure. Chnical cases have been fre- 

 quently quoted in which lesions of the region of the calcarine 

 fissure were followed by a more or less complete hemiopia. The 

 accumulated evidence on the clinical side in recent years seems 

 to have demonstrated the fact that the retinas are projected or 

 localized upon the mesial cortex of the occipital lobe in a defi- 

 nite way, the upper halves of the retinas being represented in the 

 area above the calcarine fissure and the lower halves of the ret- 



Fig. 93. — Perimeter fields in quadrant hemianopia. The outline of the visual fields 

 18 given by the dotted lines. Blindness in the left upper quadrants; cortical lesion in and 

 below the "calcarine fissure (taken from Beevor and Collier). 



inas in the area below the fissure. The macular or foveal re- 

 gion, that is, the region of distinct vision, is represented in the 

 cortex at the posterior extremity of the fissure. The localization, 

 therefore, is such that in the retina of the right eye, for example, 

 the center or foveal region is projected upon the cortex round 

 the posterior extremity of the fissure and the peripheral portions 

 of the retina extend more and more anteriorly, the upper quad- 

 rant above and the lower quadrant below the calcarine fissure. | 

 The Function of the Lower Visual Centers. — The first ending 

 of the optic fibers lies in the lateral geniculate and to a lesser 

 extent in the thalamus and superior colliculus. It is conceiv- 

 able, of course, that some degree of visual sensation may be 



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

 t Flechsig, "Locahsation der geistigen Vorgange," Leipzig' 1896. 

 JFor references to hterature see Horrax, "Physiological Reviews," 1, 

 269. 1921. 



