CHAP, ii.] THE BRAIN. 1017 



but the central machinery is not thereby affected, though its 



of usefulness is limited, and no giddiness is experienced ; and so 



in other instances. 



645. Forced Movements. So far we have dwelt on disorders 

 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 interference 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 incessantly round 

 the longitudinal axis of its own body. This is especially common 

 after section of one of the crura cerebri, or of the 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 operated on. Another form is 

 that in which the animal executes ' circus movements,' i.e. con- 

 tinually moves round and round in a circle of longer or shorter 

 radius, sometimes towards and sometimes 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 posterior 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 stnatum even when 

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

 of these forced movements may 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 executes not 

 a natural movement but a forced one, turning round or rolling 



