“3. Lateral hemianopsia, or sector-like defects of the same geometric order, with hemianæsthesia and choreiform or ataxic movements of one-half of the body without marked hemiplegia, is probably due to lesion of the caudo-lateral part of the thalamus or of the caudal division of the internal capsule (vide Fig. 7). “4. Lateral hemianopsia, with complete hemiplegia (spastic after a few weeks) and hemianæsthesia, is probably caused by an extensive lesion of the internal capsule in its central and caudal part. “5. Lateral hemianopsia, with typical hemiplegia (spastic after a few weeks), with aphasia if the right side be paralyzed, and with little or no anæsthesia, is quite certainly due to an extensive superficial lesion in the area supplied by the middle cerebral artery; we should expect to find softening of the speech-centre, of the motor zone and of the gyri lying at the extremity of the fissure of Sylvius—viz. the gyrus supramarginalis, inferior parietal lobule, and gyrus angularis. Embolism or thrombosis of the middle cerebral artery would be the most likely pathological cause of the softening. “6. Lateral hemianopsia, with moderate loss of power in one-half of the body if associated with impairment of muscular sense, but without ordinary anæsthesia, would probably be due to a lesion of the inferior parietal lobule and gyrus angularis, with their subjacent white substance, penetrating deeply enough to sever or compress the optic fasciculus in its way caudad to the visual centre. “7. Lateral hemianopsia, without motor or common sensory symptoms; this symptom alone, is due, we believe from the convincing evidence afforded by Cases 28, 29, 41, and 45, to lesions of the cuneus only, or of it and of the gray matter immediately surrounding it on the mesal surface of the occipital lobe in the hemisphere opposite the dark half-fields. Most surgical cases of lateral hemianopsia come at once or after convalescence within this rule, or No. 6.”[11] [Footnote 11: Seguin, _op. cit._] The cortical visual area, as above defined, is supplied by one large vessel—viz. the occipital artery, a branch of the posterior cerebral. Embolism or thrombosis of the former vessel is to be thought of as the probable cause of a suddenly-developed lateral hemianopsia without paralysis or anæsthesia. (_ε_) The cortical centre for sensory impressions of muscular sense, so called, is probably located in the inferior parietal lobule. The diagnosis of a lesion so placed, in a case presenting along with other sensory or with motor symptoms marked impairments of muscular sense in the arm and leg of one side, is justified by a few recent cases.[12] Spitzka {86} believes that he has clinically and pathologically demonstrated a basal path (fasciculus) for this mode of sensibility in the pons and oblongata, dorsad of the pyramidal tracts.[13]