FUNCTIONS OP THE CEREBELLUM. 307 



ment of each step; if we do think at all about our walking 

 the cerebral hemispheres simply send a message to the cere- 

 bellum, and leave it (with the aid of the spinal cord) to 

 regulate all the details. When we walk without thinking 

 about it, the contact of the foot with the ground stimulates 

 sensory nerves of the sole, which then stimulate the locomotor 

 centres; these centres excite in proper order the nerves 

 which control the muscles; and the co-ordinated action of 

 the muscles produces the next step. 



A pigeon with its cerebellum destroyed and all the rest 

 of its nervous system intact stands unsteadily, staggers when 

 it attempts to walk, and flutters uselessly when thrown 

 into the air. But, having its cerebrum, it wills and feels; 

 it does not stand quiet until touched; it initiates movements 

 when left to itself, though it cannot perform them properly. 

 It wills, and feels, and thinks, but cannot co-ordinate the 

 action of its muscles except for some simple movements, 

 regulated by the medulla oblongata or the spinal cord. 



Automatic Nerve-Centres send out nervous impulses 

 through efferent nerves without waiting to be excited by 

 afferent nerves or by the Will. The most conspicuous are 

 the small nerve-centres buried in the heart, which excite its 

 beat even when it is separated from all the rest of the body. 

 Another automatic centre is that which lies in the medulla 

 oblongata and stimulates the nerves which control the 



Do we have to think about using each muscle concerned in walk- 

 ing? What happens when we think about our walking? What when 

 we walk without thinking about it ? 



What do we see in a pigeon whose cerebellum has been destroyed? 

 Does it initiate movements? Does it execute them well? What Is 

 its condition as regards willing, feeling, and thinking? What can 

 it not do? 



What is done by automatic nerve-centres? Give examples of au- 

 tomatic nerve-centres. 



