SENSE AREAS AND ASSOCIATION AREAS. 211 



quadrants of the retina, and is designated frequently as quadrant 

 hemiopia (see Fig. 93). It has been assumed that the fibers from 

 the fovea end perhaps in the fissure itself according to some 

 authors (Henschen) , along the anterior third of the fissure, according 

 to others (Schmid and Laqueur*) along the posterior portion of the 

 fissure. Moreover, since unilateral lesions in this region, however 

 extensive, do not cause complete blindness in the fovea, it has 

 been supposed that this important part of the retina is bilaterally 

 represented in the cortex, so that complete foveal blindness 

 that is, blindness of the centers of the visual fields can only 

 occur when both occipital lobes are injured in the region of the 

 calcarine fissure. While 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. Those who hold this view 

 explain the known fact that lesions in the region of the calcarine 

 fissure give the most permanent condition of hemiopia, on the 

 view that these lesions involve the underlying fibers of the 

 occipitothalamic radiation. Monakow,f for instance, points 

 out that while extensive lesions of the occipital cortex on both 

 sides leave, with a few exceptions, some degree of central vision, 

 no cases are reported of cortical lesions involving only or mainly 

 the vision in the macular region. He, therefore, argues that 

 while the paths from the retina to the lower visual centers 

 (lateral geniculate) may be isolated, the further connections 

 with the cortex must be widespread. The cortical center for 

 distinct vision according to this view is not limited to a narrow 

 area, but must involve a large region in the occipital cortex. 

 It is difficult to reconcile this view with the ideas of isolated 

 conduction and specific function of each part of the cortex. Some 

 additional facts of interest have been obtained from experiments 

 involving the stimulation of the occipital cortex. Stimulation 

 of this kind causes movements of the eyes, and the movements 

 vary with the place stimulated. J Stimulation of the upper border 

 of the lobe causes movements of the eyes downward, stimulation 

 of the lower border movements upward, and of intermediate regions 

 movements to the side. Assuming that the direction of the move- 

 ment is to ward -that part of the visual field from which a normal 

 visual stimulus would come, it is evident that movements of the 



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



t Monakow, loc. cit., also "Ergebnisse d. Physiologic," 1907. 



j Schafer, "Brain," 11, 1, 1889, and 13, 165, 1890. 



