430 Anatomy Applied to Medicine and Sutgeiy. 



Superior parietal lobule. A tumor, here, interferes 

 with sensation, while one affecting the inferior parietal 

 lobule, and especially the angular gyrus, will cause word 

 blindness, particularly when the left gyrus is affected. 



A tumor involving the occipital lobe, and especially 

 the mesial surface of it, i.e., the cuneus, induces disturb- 

 ance of vision. The visual tract passes from /the occipital 

 lobe forwards, as the optic radiation, through the pos- 

 terior part of the internal capsule, to the pulvinar of the 

 optic thalamus and to the geniculate bodies and the cor- 

 pora quadrigemina, and thence, beneath the crus cerebri as 

 the optic tract, to decussate with the opposite tract at the 

 optic chiasma. Hence the fibres from the right occipital 

 lobe supply the right half of the retina, and, those from 

 the left, the left half of the retina, so that a tumor affect- 

 ing the right occipital lobe, or its neighborhood, or press- 

 ing on the right visual radiation, will destroy the action of 

 the right halves of the retinae, thus causing blindness on 

 the nasal side of the left retina and on the temporal side of 

 the right, i.e., left lateral homonymous hemianopsia. 



Tumors of the temporal lobe may produce interference 

 with word hearing, especially if the left be affected, or, if 

 on the under surface, according to Ferrier, disturbance of 

 smell and taste. 



Tumors in the fissure of Sylvius and upon the island 

 of Reil produce numerous symptoms because of their 

 pressure on contiguous structures; thus, on the hinder 

 end of the third frontal they cause motor aphasia and 

 agraphia ; on the operculum, facial paralysis ; on the su- 

 perior and middle temporal, word deafness ; on the island 

 of Reil and underlying external capsule, paraphasia, i.e., 

 interference with speech due. to destruction of the conduc- 

 tion areas for the different regions associated in speech. 

 Interference with speech, like word deafness and word 



