THE CEREBRUM. 503 



of the occipital lobe together with the angular gyrus gave rise to a 

 more or less enduring hemianopsia, in addition to the transient 

 blindness of the opposite eye. From these and similar facts he con- 

 cluded that the angular gyrus is the area of representation for the 

 macular or central region of the retina, and the occipital lobe for 

 the corresponding halves of the peripheral portions of the retina. 



It was, however, found by Munk, Schafer, and others that the 

 angular gyrus was not concerned in any way with vision; that extir- 

 pation of the occipital lobe alone, especially if the line of division 

 be carried a little further forward on the mesial and inferior sur- 

 faces, was followed by homonymous hemiopia (loss of retinal func- 

 tion on the same side), and therefore homonymous hemianopsia. 

 Additional experiments lead to the conclusion that the area for 

 macular vision is near the anterior extremity of the calcarine fissure, 

 while the area for peripheral vision is in the posterior portion of the 

 mesial surface and for a variable distance on the outer surface. 

 Moreover, there is reason to believe that the area for macular vision 

 is in relation with homonymous halves of the two maculae lutese. 

 The supposed error, the assignment of macular vision to the angular 

 gyrus, has been attributed to destruction of the fibers of the optic 

 radiation, which in their course to the occipital lobe pass close to 

 this gyrus. 



Electric stimulation of the sensor areas is attended by certain 

 motor reactions which vary in accordance with the area stimulated. 

 Thus, when the electrodes are applied to different portions of the 

 occipital lobe the eyeballs are conjugately turned upward, downward, 

 or laterally and to the opposite side; when placed on the upper por- 

 tion of the superior temporal convolution, the ear is pricked up or 

 retracted, the head is turned to the opposite side and the pupils 

 are dilated ; when placed on the hippocampal convolution, there is 

 movement of torsion of the nostril and lips of the same side. 



Ferrier assumed that these movements were the result of the 

 origination of subjective sensations and not an evidence that the 

 area in question is a motor area, in the sense that this term is applied 

 to the areas of the Rolandic region, especially as their destruction 

 is not followed by paralysis of any of the corresponding muscles. 

 This interpretation is supported by the experiments of Schafer, 

 which showed that the contraction of the eye-muscles which followed 

 stimulation of the occipital lobe took place between 0.2 and 0.3 



ness" in r the opposite half of the field of vision the name hemianopsia is given. In 

 the lesion under consideration (division of one optic tract) the hemianopsia is bilateral, 

 and as it affects the corresponding portions associated in normal vision it is of the 

 homonymous variety. Division of the right optic tract is followed by left lateral homon- 

 ymous hemianopsia, indicative of the fact that objects in the field of vision to the 

 left of the binocular fixation point are invisible. 



