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One of the most instructive proofs of motor localization in the cortex is that furnished by the disease now called aphemia, or motor aphasia. Motor aphasia is neither loss of voice nor paralysis of the tongue or lips. The patient's voice is as strong as ever, and all the innervations of his


FIG. 43.-Schematic transverse section of the human brain, through the rolandic region. S, fissure of Sylvius; N.C., nucleus candatus, and N.L., nucleus lenticularis, of the corpus striatum; O.T., thalamus; C, crus; M, medulla oblongata; VII, the facial nerves passing out from their nucleus in the region of the pons. The fibres passing between O.T. and N.L. constitute the socalled internal capsule.

hypoglossal and facial nerves, except those necessary for speaking, may go on perfectly well. He can laugh and cry, and even sing; but he either is unable to utter any words at all; or a few meaningless stock phrases form his only speech; or else he speaks incoherently and confusedly,

mispronouncing, misplacing, and misusing his words in various degrees. Sometimes his speech is a mere broth of unintelligible syllables. In cases of pure motor aphasia the patient recognizes his mistakes and suffers acutely from them. Now whenever a patient dies in such a condition as this, and an examination of his brain is per

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FIG. 44.-Schematic profile of left hemisphere, with the parts shaded whose destruction causes motor ('Broca') and sensory (Wernicke ') aphasia.

mitted, it is found that the lowest frontal gyrus (see Fig. 44) is the seat of injury. Broca first noticed this fact in 1861, and since then the gyrus has gone by the name of Broca's convolution. The injury in right-handed people is found on the left hemisphere, and in left-handed people on the right hemisphere. Most people, in fact, are left-brained, that is, all their delicate and specialized movements are handed over to the charge of the left hemisphere. The ordinary right-handedness for such movements is only a consequence of that fact, a consequence which shows out

wardly on account of that extensive crossing of the fibres from the left hemisphere to the right half of the body only, which is shown in Fig. 41, below the letter M. But the left-brainedness might exist and not show outwardly. This would happen wherever organs on both sides of the body could be governed by the left hemisphere; and just such a case seems offered by the vocal organs, in that highly delicate and special motor service which we call speech. Either hemisphere can innervate them bilaterally, just as either seems able to innervate bilaterally the muscles of the trunk, ribs, and diaphragm. Of the special movements of speech, however, it would appear (from these very facts of aphasia) that the left hemisphere in most persons habitually takes exclusive charge. With that hemisphere thrown out of gear, speech is undone; even though the opposite hemisphere still be there for the performance of less specialized acts, such as the various movements required in eating.

The visual centre is in the occipital lobes. This also is proved by all the three kinds of possible evidence. It seems that the fibres from the left halves of both retinæ go to the left hemisphere, those from the right half to the right hemisphere. The consequence is that when the right occipital lobe, for example, is injured, hemianopsia' results in both eyes, that is, both retinæ grow blind as to their right halves, and the patient loses the leftward half of his field of view. The diagram on p. 111 will make this matter clear (see Fig. 45).


Quite recently, both Schaefer and Munk, in studying the movements of the eyeball produced by galvanizing the visual cortex in monkeys and dogs, have found reason to plot out an analogous correspondence between the upper and lower portions of the retina and certain parts of the visual cortex. If both occipital lobes were destroyed, we should have double hemiopia, or, in other words, total blindness. In human hemiopic blindness there is insensibility to light on one half of the field of view, but

mental images of visible things remain. In double hemiopia there is every reason to believe that not only the sensation of light must go, but that all memories and images

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FIG. 45.-Scheme of the mechanism of vision, after Seguin. The cuneus convolution (Cu) of the right occipital lobe is supposed to be injured, and all the parts which lead to it are darkly shaded to show that they fail to exert their function. F.O. are the intra-hemispheric optical fibres. P.O.C. is the region of the lower optic centres (corpora geniculata and quadrigemina). T.O.D. is the right optic tract; C, the chiasma; F.L.D. are the fibres going to the lateral or temporal half T of the right retina, and F.C.S. are those going to the central or nasal half of the left retina. O.D. is the right, and O.S. the left, eyeball. The rightward half of each is therefore blind; in other words, the right nasal field, R.N.F., and the left temporal field, L.T.F., have become invisible to the subject with the lesion at Cu.

of a visual order must be annihilated also. The man loses his visual ideas.' Only cortical' blindness can produce this effect on the ideas. Destruction of the retina or of the visual tracts anywhere between the cortex and the eyes impairs the retinal sensibility to light, but not the power of visual imagination.

Mental Blindness.-A most interesting effect of cortical disorder is mental blindness.

This consists not so much


FIG. 46.-Fibres associating the cortical centres together. (Schematic, after


in insensibility to optical impressions, as in inability to understand them. Psychologically it is interpretable as loss of associations between optical sensations and what they signify; and any interruption of the paths between the optic centres and the centres for other ideas ought to bring it about. Thus, printed letters of the alphabet, or words, signify both certain sounds and certain articulatory movements. But the connection between the articulating or auditory centres and those for sight being ruptured, we ought a priori to expect that the sight of words would

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