THE REGULATING MECHANISM 203 



There is no automatism, at all events in 

 the nervous centres, but rather a series of 

 changes induced by the quantity and the 

 quality of the blood and by nervous impulses 

 from many quarters Thus the body works 

 as a whole. There is no autocratic centre ; 

 the most autocratic, the cerebrum itself, the 

 seat of what we term the will, comes under 

 the same law. 



116. The pons consists mainly of great trans- 

 verse bands of fibres passing from one side of 

 the cerebellum to the other. In it there are 

 bundles of fibres passing upwards and down- 

 wards and masses of grey matter for some 

 of the roots of cranial nerves. The pons is 

 intimately related to the cerebellum, as the 

 transverse fibres form what are known as the 

 middle peduncles of that organ. 



117. Immediately above the pons we find 

 the crura or peduncles of the brain, containing 

 the great motor and sensory paths. They 

 also contain numerous fibres connecting the 

 cerebellum with the cerebrum. Near the 

 peduncles we find four small bodies, the 

 corpora quadrigemina. These consist of layers 



