THE MACHINERY OF COORDINATED MOVEMENTS. 649 



tinctly conscious of this disaccord ; the visual sensations are so prepotent in 

 consciousness that we really think the external world is rapidly whirling 

 round ; all that we are further conscious of is the feeling of giddiness and our 

 inability to make our bodily movements harmonize with our visual sensations. 

 So that even in the cases where the loss of coordination is brought about by 

 distinct sensations, what we really appreciate by means of our consciousness 

 is the disarrangement of the coordinating machinery. It is the apprecia- 

 tion of this disorder which constitutes the feeling of vertigo ; both the feel- 

 ing of giddiness and the disordered movements are the outcome, one sub- 

 jective and the other objective, of the same thing. It is not because we 

 feel giddy that we stagger and reel ; our movements are wrong because the 

 machinery is at fault, and it is the faulty action of the machinery which also 

 makes us feel giddy. 



We may here perhaps remark that it is an actually disordered condition 

 of the coordinating mechanism which gives rise to the affection of conscious- 

 ness which we call giddiness, not a mere curtailing of the mechanism or any 

 failure on its part to make itself effective. Complete blindness limits the 

 range of activity of the machinery but leaves the remainder intact, and no 

 giddiness is felt. So again in certain diseases of the nervous system the 

 muscular sense is interfered with over considerable regions of the body, and 

 in these regions coordination fails or is imperfect, but the central machinery 

 is not thereby affected, though its area of usefulness is limited, and no giddi- 

 ness is experienced ; and so in other instances. 



558. Forced movements. So far we have dwelt on disorders of the co- 

 ordinating machinery brought about by the action of various afferent im- 

 pulses. 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 ob- 

 served, 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 wit- 

 nessed after injury to the bulb and corpora quadrigemina. Sometimes the 

 animal rotates toward and sometimes away from the side operated on. An- 

 other 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 toward and sometimes away from the injured side. This may be 

 seen after several of the above-mentioned operations, and in one form or an- 

 other is not uncommon after various unilateral injuries to the brain. There 

 is a variety of the circus movement, the " clock-hand 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 backward 

 or forward 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 gray matter is affected. And many of these 



