. 



CHAP, ii.] THE BRAIN. 735 



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480. Forced Movements. So far we have dwelt on disor- 

 ders of the coordinating machinery brought about by the action 

 of various afferent impulses. We have now to call attention 

 to some peculiar phenomena which result from operative inter- 

 ference with parts of the brain, and which in some instances 

 at least may be taken to illustrate how this complex machinery 

 works when some of its inner wheels are broken. 



All investigators who have performed experiments on the 

 brain have observed, as the result of injury to various parts of 

 it, remarkable movements which have the appearance of being 

 irresistible, compulsory, forced. They vary much in the extent 

 to which they are developed ; some are so slight as hardly to 

 deserve the name, while others are strikingly intense. One of 

 the most common forms is that in which the animal rolls inces- 

 santly round the longitudinal axis of its own body. This is 

 especially common after section of one of the crura cerebri, or 

 of tiie middle and inferior peduncles of the cerebellum, or after 

 unilateral section of the pons, but has also been witnessed after 

 injury to the bulb and corpora quadrigemina. Sometimes the 

 animal rotates towards and sometimes away from the side oper- 

 ated on. Another form is that in which the animal executes 

 'circus movements,' i.e. continually moves round and round in 

 a circle of longer or shorter radius, sometimes towards and some- 

 times away from the injured side. This may be seen after several 

 of the above-mentioned operations, and in one form or another 

 is not uncommon after various unilateral injuries to the brain. 

 There is a variety of the circus movement, ' the clockhand 

 movement,' said to occur frequently after lesions of the poste- 

 rior corpora quadrigemina, in which the animal moves in a 

 circle, with the longitudinal axis of its body as a radius, and 

 the end of its tail for a centre. And this form again may easily 

 pass into a simple rolling movement. In yet another form the 

 animal rotates over the transverse axis of its body, tumbles head 

 over heels in a series of somersaults ; or it may run incessantly 

 in a straight line backwards or forwards until it is stopped by 

 some obstacle. These latter forms of forced movements are 

 sometimes seen after injury to the corpus striatum, even when 

 a very limited portion of the grey matter is affected. And many 

 of these forced movements m&y result from injuries which appear 

 to be confined to the cerebral cortex. 



When the phenomena are well developed, every effort of 

 the animal brings on a movement of this forced character. Left 

 to itself and at rest the animal may present nothing abnormal, 

 its posture and attitude may be quite natural ; but when it is 

 excited to move or when it attempts of itself to move, it exe- 

 cutes not a natural movement but a forced one, turning round 

 or rolling over as the case may be. In severe cases the move- 

 ment is continued until the animal is exhausted; when the 



