THE CENTRAL NERVOUS SYSTEM 837 



destroyed (Ewald). The observation of Rawitz, that the peculiar 

 rotatory movements of the so-called Japanese dancing mice are 

 associated with marked anatomical peculiarities in the labyrinth, is 

 another fact in favour of the connection of the canals with the 

 maintenance of equilibrium and the sense of rotation. So is the 

 relation between the degree of development of the canals in different 

 species of birds and the degree of agility in the co-ordination of 

 their movements (Laudenbach) . 



But forced movements may also follow injuries (especially uni- 

 lateral) to many portions of the brain e.g., the pons, crus cerebri, 

 posterior corpora quadrigemina, corpus striatum, even the cerebral 

 cortex, and above all the cerebellum. The movements are of the 

 most various kinds. The animal may run round and round in a circle 

 (circus movement) ; or, with the tip of its tail as centre and the 

 length of its body as radius, it may describe a circle with its head, as 

 the hand of a clock does (clock-hand movement) ; or it may rush 

 forward, turning endless somersaults as it goes. Intervals of rest 

 alternate with paroxysms of excitement, and the latter may be 

 brought on by stimulation. In man forced movements associated 

 with vertigo have been sometimes seen in cases of tumour of the 

 cerebellum e.g., involuntary rotation of the body in tumour of the 

 middle peduncle. No entirely satisfactory explanation of these 

 forced movements has been given. They are evidently connected 

 with disturbance of the mechanism of co-ordination, leading to a 

 loss of proportion in the amount of the motor discharge to muscles 

 or groups of muscles accustomed to act together in executing definite 

 movements. For instance, in circus movements the muscles of the 

 outer sides of the body contract more powerfully than those of the 

 inner side, and the animal is therefore constrained to trace a circle 

 instead of a straight line, the excess of contraction on the outer side 

 being analogous to the acceleration along the radius in the case of a 

 point moving in a circle. 



Co-ordination of Movements. The capacity of executing some 

 co-ordinated movements, occasionally of considerable complexity, 

 seems to be inborn in man, and to a still greater extent in many of 

 the lower animals. The new-born child brings with it into the world 

 a certain endowment of co-ordinative powers ; it has inherited, for 

 example, from a long line of mammalian ancestors the power of 

 performing those movements of the cheeks, lips, and tongue, on 

 which sucking depends ; perhaps from a long, though somewhat 

 shadowy, race of arboreal ancestors the power of clinging with hands 

 and feet, and thus suspending itself in the air. Many movements, 

 such as walking and the co-ordinated muscular contractions involved 

 in standing, and even in sitting, which, once acquired, appear so 

 natural and spontaneous, have to be learnt by painful effort in the 

 hard school of (infantile) experience. Most people learn, and are 

 willing to confess that they have learnt, to execute a considerable 

 number of co-ordinated movements with the arms, and especialty 

 with the fingers ; but few have considered that the extreme dexterity 

 of jaws, tongue, and teeth displayed by a hungry mouse or school- 

 boy is the result of the much practice which maketh perfect. The 

 exquisite co-ordination of the muscles of the eyeball, which we 

 shall afterwards have to speak of, and the no less wonderful balance 

 of effort and resistance, of power put forth and work to be done, of 

 which we have already had glimpses in studying the mechanism 

 of voice and speech, become to a great extent the common property 



