ENCEPHALIC SEAT OF MUSCULAR MOTION. 



393 



under such circumstances, the animal frequently remained with its paws 

 in the air, and ate in this attitude. What he conceives to have been 

 one of his most singular experiments was, the effect of the division 

 of the cerebellum into two lateral and equal halves : the animal ap- 

 peared to be alternately impelled to right and left, without retaining 

 any fixed position: if he made a turn or two on one side, he soon 

 changed his motion and made as many on the other. M. Serres 1 who 

 is well known as a writer on the comparative anatomy of the brain, and 

 must have had unusual opportunities for observation at the Hospital La 

 Pitie to which he was attached gives the case of an apoplectic, who 

 presented, amongst other symptoms, the singular phenomenon of turn- 

 ing round, like the animals in those experiments; and, on dissection, an 

 apoplectic effusion was found in that part of the encephalon. On di- 

 viding the pons Varolii vertically, from before to behind, M. Magendie 2 

 found, that the same rotary movement was produced : when the section 

 was to the left of the median line, the rotation was to the left, and con- 

 versely; but he could never succeed in making the section accurately 

 on the median line. From these facts he concludes, that there are two 

 forces, which are equilibrious by passing across the circle formed by the 

 pons Varolii and cerebellum. To put this beyond all question, he cut 

 one peduncle, when the animal immediately rolled in one direction; but 

 on cutting the other or the one on the opposite side, the movement 

 ceased, and the animal lost the power of keeping itself erect, and of 

 walking. 



From the results of all his experiments, M. Magendie infers, that an 

 animal is a kind of automatic machine, wound up for the performance 

 of certain motions, but incapable 

 of producing any other. The 

 figure of the base of the brain 

 in the margin, will explain, more 

 directly, the impulses described 

 by this physiologist. The cor- 

 pora striata are situate in each 

 hemisphere, but their united 

 impulses may be represented by 

 the arrow A; the impulse seated 

 in the cerebellum, by the arrow 

 B ; and those in each peduncle 

 of the cerebellum, p, p, by the 

 arrows C and D respectively. 

 When the impulse backwards is 

 from any cause destroyed, the 

 animal is given up to the forward 

 impulse, or that represented by 

 the arrow B; and conversely. 

 In like manner, the destruction 

 of one lateral impulse leaves the 

 other without an antagonist, and 



Fig. 165. 



Direction of Encephalic Impulses, according to 

 M 



1 Magendie's Journ. de Physiol., iv. 405. 



[agendie. 

 3 Precis, &c., p. 344. 



