. Cosmic law; the immortality of the soul and the existence of God. Fig. 20. Diagram. Comparatively recent anatomical discoveries have demon-strated a number of important facts concerning the relationof the brain-structure to the mind and to the voluntaryactivities of the body: 1.—One of these facts is, that par-ticular tracts of the cerebral cortex (in both hemispheres),through which muscular control is exercised by the will, havebeen identified and located; so it is now possible to make amap showing the location of many of these tracts and approx-imately defining their boundaries. As these m
. Cosmic law; the immortality of the soul and the existence of God. Fig. 20. Diagram. Comparatively recent anatomical discoveries have demon-strated a number of important facts concerning the relationof the brain-structure to the mind and to the voluntaryactivities of the body: 1.—One of these facts is, that par-ticular tracts of the cerebral cortex (in both hemispheres),through which muscular control is exercised by the will, havebeen identified and located; so it is now possible to make amap showing the location of many of these tracts and approx-imately defining their boundaries. As these motor-regions are in duplicates (one for each 256 THE HUMAN BEAIN. THE HUMAN BEAIN 257 hemisphere) and both are normally active; and, as intraversing the brain-stem the nerves of each hemisphere crossto the opposite side, it results that if the right hemispherebe seriously injured in its motor region the limbs on theleft side will be paralyzed, and if the left hemisphere be in-jured the limbs on the right side will be paralyzed. If theinjury is confined to a single tract of the motor-region, theparalysis is confined to the limb or member controlled bythat tract. So that now, when a surgeon is called to a caseof right or left paralysis, he has only to ascertain what limbsor members are affected, in order to determine the localitywhere the injury was suffered in the opposite hemisphere. 2.—The second fact recently discovered is, that the pure-ly-intellectual or mental faculties occupy other definite tractsof the brain-cortex, hut in only one of the two hemispheres;and that thus we do all our thinking in only one half of thebrain. This is at once illu
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