Organic and functional nervous diseases; a text-book of neurology . acob, Das Menschenhirn.) or blindness in one-half of both eyes, each hemisphere of the brainreceiving impressions from the opposite visual fields. The exactanatomy of the optic nerves and optic tracts will be considered inChapter XXXV. Suffice it here to mention that each optic tractends in the pulvinar of the optic thalamus, in the external geniculatebody, and in the corpus quadrigeminum anterior (Fig. 58), and thatfrom these ganglia the visual tract issues into the posterior fifth of the LOCAL SYMPTOMS. 121 internal capsule,
Organic and functional nervous diseases; a text-book of neurology . acob, Das Menschenhirn.) or blindness in one-half of both eyes, each hemisphere of the brainreceiving impressions from the opposite visual fields. The exactanatomy of the optic nerves and optic tracts will be considered inChapter XXXV. Suffice it here to mention that each optic tractends in the pulvinar of the optic thalamus, in the external geniculatebody, and in the corpus quadrigeminum anterior (Fig. 58), and thatfrom these ganglia the visual tract issues into the posterior fifth of the LOCAL SYMPTOMS. 121 internal capsule, and turning backward in it passes through the cen-trum ovale, outside of the posterior horn of the lateral ventricle, andterminates in the cortex of the occipital lobe. Tlie exact terminationof these fibres is in the cortex about the calcarine fissure and in thecuneus, a wedge-shaped lobule on the median surface of the hemi-sphere. (Fig. 60.) But the convolutions of the convexity of theoccipital lobe are also concerned in the reception and storing up of Fig. Lesions of the occipital lobe causing hemianopsia. (From Heuschen.) visual impressions, and hence lesions in any part of the occipital cortexare productive of hemianopsia. There seems to be a projection of the visual field to some extentupon the cortex of the cuneus, for small lesions there may cause smallsector-like defects in the visual field. Henschen, in his elaborate workon the putliology of the brain, has confirmed this conclusion, whichWilbrandt and Hun liad reached from a smaller number of cases. 122 DIAGNOSIS AND LOCALIZATION OF BBAiN DlSHASES. Fig. 59, 17, shows the location of the lesion in Huns case. Thedefect in the visual fields in this patient was limited to the upperquadrant. Lesions in the upper part of the cuneus cause blindness inthe lower quadrant of both visual fields, and lesions in the lower partof the cuneus cause blindness in the upper quadrant of both visualfields. It is rare for a lesion, ho
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