. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . he same system oflocalization. The anatomical meth-od lends further support to the sameconclusion; for it is after lesion ofthe precentral gyre that the pyram-idal or cortico-spinal tracts de-generate. And since there is nodoubt that these tracts are the prin-cipal motor path (Fig. 103) of con-nection between the cortex and thecord, their origin from the precen-tral gyre is strong evidence that thisgyre is the true motor area. Aspecially favorable opp
. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . he same system oflocalization. The anatomical meth-od lends further support to the sameconclusion; for it is after lesion ofthe precentral gyre that the pyram-idal or cortico-spinal tracts de-generate. And since there is nodoubt that these tracts are the prin-cipal motor path (Fig. 103) of con-nection between the cortex and thecord, their origin from the precen-tral gyre is strong evidence that thisgyre is the true motor area. Aspecially favorable opportunity forexamining this question is affordedby cases of the disease known asamyotrophic lateral disease produces at the sametime a gradual atrophy of the mus-cles, and also progressive degenera-tion of those portions of the nervous system which are connectedwith the muscles; namely, of the cells of the ventral horn of the cord,and of the cortico-spinal tract throughout its whole extent. Ac-cordingly the origin of these motor tracts in the cortex ought to besimilarly affected; and recent careful examination by several au-. Fia. 103.—Diagram of the Motor Path-way from the Cortex. 240 THE CEREBRAL HEMISPHERES thorities* has shown that, in fact, the cortex of the precentral gyreshows profound pathological changes in cases ofthis disease. Thegiant cells, which are characteristic of this gyre, are very muchreduced in number, and the other cells are also affected. The largefibres which issue from the cortex and which pass—many of themat least—downward to form the pyramidal tracts have largelydisappeared; but no corresponding changes are found in the post-central gyre. The bottom of the central fissure is,- by this method,indicated as being, in the huiiian brain, the hinder boundary ofthe motor region; and although the forward boundary is less sharplydefined, the changes are for the most part confined to the precentralgyre. Still more convincing is the experimen
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