528 HANDBOOK OF PHYSIOLOGY. 



will upon them; and it must be admitted that all the facts just referred 

 to are as well explained on this hypothesis as on that of the cerebellum 

 being the organ for combining movements. A harmonious combination 

 of muscular actions must depend as much on the capability of appreciat- 

 ing the condition of the muscles with regard to their tension, and to the 

 force with which they are contracting, as on the power which any special 

 nerve-centre may possess of exciting them to contraction. And it is be- 

 cause the power of such harmonious movement would be equally lost, 

 whether the injury to the cerebellum involved injury to the seat of mus- 

 cular sense, or to the centre for combining muscular actions, that ex- 

 periments on the subject afford no proof in one direction more than the 

 other. 



Forced Movements. The influence of each half of the cerebellum 

 is directed to muscles on the opposite side of the body; and it would ap- 

 pear that for the right ordering of movements, the actions of its two 

 halves must be always mutually balanced and adjusted. For if one of 

 its crura, or if the pons on either side of the middle line, be divided, so 

 as to cut off from the medulla oblongata and spinal cord the influence of 

 one of the hemispheres of the cerebellum, strangely disordered move- 

 ments ensue (forced movements). The animals fall down on the side 

 opposite to that on which the crus cerebelli has been divided, and then 

 roll over continuously and repeatedly; the rotation being always round 

 the long axis of their bodies, and generally from the side on which the 

 injury has been inflicted. The rotations sometimes take place with much 

 rapidity; as often, according to Magendie, as sixty times in a minute, 

 and may last for several days. Similar movements have been observed 

 in men; as by Serres in a man in whom there was apoplectic effusion in 

 the right crus cerrebelli; and by Bellhomme in a woman, in whom an 

 exostosis pressed on the left crus. They may, perhaps, be explained by 

 assuming that the division or injury of the crus cerebelli produces para- 

 lysis or imperfect and disorderly movements of the opposite side of the 

 body; the animal falls, and then, struggling with the disordered side on 

 the ground, and striving to rise with the other, pushes itself over; and 

 so again and again, with the same act, rotates itself. Such movements 

 cease when the other crus cerebelli is divided; but probably only because 

 the paralysis of the body is thus made almost complete. Other varieties 

 of forced movements have been observed, especially those named " cir- 

 cus movements," when the animal operated upon moves round and 

 round in a circle; and again those in which the animal turns over and 

 over in a series of somersaults. Nearly all these movements may result 

 on section of one or other of the following parts; viz. crura cerebri, me- 

 dulla, pons, cerebellum, corpora quadrigemina, corpora striata, optic 

 thalami, and even, it is said, of the cerebral hemispheres. 



