Emotions are for the most part excited through the senses. A tale of woe, a dis gusting or painful spectacle, a feat of won derful power or skill, the sudden appearance of a person not expected, are calculated to produce corresponding emotions of pity, dis gust or pain, wonder or surprise. But emo tions may likewise be produced by intellectual change. The workings of the conscience may remind one of some duty neglected or some fault committed, and the emotion of pain, or pity, or remorse may ensue. Now emotion may give rise to movements indepen dently of the Will. The extraordinary influ ence of emotion on the countenance is well known, and this may affect one -side of the face, which is paralysed to the influence of the will, or it may excite movements of the limbs, even when the will can exert no controul over them. From these facts it is plain that that part of the brain which is influenced by emo tion must be so connected that the convolu tions may affect it or be affected by it; that it may be readily acted on by the nerves of pure sense; that it may influence the spinal cord and the motor nerves of the face when the ordinary channels of voluntary action have beer, stopped. No part possesses these conditions so completely as the superior and posterior part of the mesocephale, which we have already noticed as concerned in acts of sensation. Is an emotion excited by an impression made upon one of the senses ? this part becomes directly affected, and through the optic thala mus the emotional feeling causes intellectual change. The working of the intellect on the
other hand may act on the seat of emotion through the same channel. And an excite ment of this part may produce movement of a limb, or of all the limbs, through its influence on the spinal cord through the olivary columns.
The cerebellum influences the antero-lateral columns of the cord, partly through the deep fibres of its great commissure, the pons Varolii, which interlace freely with the fibres of the anterior pyramids, vesicular matter being in terposed, and partly through those portions of the restiform bodies which penetrate the antero lateral columns of the spinal cord. It asso ciates and harmonizes the movements of the trunk, and especially those of the lower ex tremities, for locomotion, through those por tions of the restiform bodies which are con tinued with the posterior columns of the cord.
The crossed influence of deep lesion of either hemisphere of the cerebellum is difficult to explain in the absence of any proved decus sation of the restiforrn bodies. The connection of the deep fibres of the pons, however, with the anterior pyramids in the mesocephale does afford some explanation. lf, for instance, the left cerebellar hemisphere be the seat of lesion, these fibres will be affected, and they may in fluence the fibres of the left pyramid, which ag,ain will affect the right half of the cord and the right side of the body. Those fibres of the restiforrn bodies which incorporate them selves with the antero-lateral columns, are doubtless too few to produce much influence.