394 MUSCULAR MOTION. 



the animal moves in the direction of the arrow placed over the seat of 

 the impulsion that remains. In a state of health, all these impulsions 

 being nicely antagonized, they are subjected to the influence of volition ; 

 but in disease they may be so modified as to be entirely withdrawn 

 from its control. 



These four are not the only movements excited by particular injuries 

 done to the nervous system. M. Magendie 1 states, that a circular mov- 

 ment to the right or left, similar to that of horses in a circus, was caused 

 by the division of the medulla oblongata, to the outer side of the cor- 

 pora pyramidalia anteriora. When the section was made on the right 

 side, the animal turned, in this fashion, to the right; and to the left, if 

 the section was made on that side. 



Pathology has, likewise, indicated the brain as the seat of different 

 bodily movements. Diseases of the encephalon have been found not 

 only to cause irregular movements or convulsions, but, also, paralysis 

 of a part of the body, leaving the rest untouched. Hence it has been 

 concluded, that every motion of every part has its starting point in 

 some portion of the brain. The ancients were well aware, that in cases 

 of hemiplegia, the encephalic cause of the affection is found in the 

 opposite hemisphere. Attempts have been made to decide upon the 

 precise part of the encephalon in which the decussation takes place. 

 Many have conceived it to be in the commissures ; but the greater num- 

 ber, perhaps, have referred it to the corpora pyramidalia. These, the 

 researches of Gall and Spurzheim 2 and others, had pointed out as de- 

 cussating at the anterior surface of the marrow, and as being apparently 

 continuous with the radiated fibres of the corpora striata; and an 

 opinion has prevailed, that the paralysis is of the same side as the 

 encephalic affection, or of the opposite, according as the affected part of 

 the brain is a continuation of fasciculi, which do not decussate of the 

 corpora olivaria, for example or of the corpora pyramidalia, which do. 

 M. Serres, 3 however, affirms, that affections of the cerebellum, pons 

 Varolii, and tubercula quadrigemina, exert their effects upon the oppo- 

 site side of the body, and he supports his statement by pathological 

 cases and direct experiment. M. Magendie 4 divided one pyramid from 

 the fourth ventricle; yet no sensible effect was produced on the move- 

 ments ; certainly, there was no paralysis, either of the affected or oppo- 

 site side: he then divided both pyramids about the middle, and no 

 apparent derangement occurred in the motions a slight difficulty in 

 progression being alone observable. The section of the posterior pyra- 

 mids was equally devoid of perceptible influence on the general move- 

 ments; and to cause paralysis of one half the body, it was necessary 

 to divide the half of the medulla oblongata, when the corresponding 

 side became, not immovable, for it was affected by irregular move- 

 ments ; and not insensible, for the animal moved its limbs when they 

 were pinched, but incapable of executing the determinations of the 

 will. 



These views are not exactly in accordance with the general idea, 



' Precis, &c., p. 345. 



3 Recherches sur le Systeme Nerveux, &c., sect, vi., Paris, 1809. 



9 Anatomie Compares du Cerveau, Paris, 1824. 4 Op. cit. 



