524 THE XERVOUS SYSTEM. 



and involuntary, anyone may convince himself by trying 

 to perform, each individual movement concerned, strictly 

 as a voluntary act. 



That such movements are reflex and essentially inde- 

 pendent as regards their mere production of the will, 

 there is no doubt : that the nerve-centres through which 

 such reflex actions are performed are the so-called sensory 

 ganglia, is, of course, only a theory which may or not be 

 confirmed by future investigations. 



Besides their possible functions in the manner just men- 

 tioned, it is supposed that these sensory ganglia may be 

 the means of transmitting the impulses of the will to the 

 muscles, which act in obedience to it, and thus be the 

 centres of reflex action as well for impressions conveyed 

 downwards to them from the cerebral hemispheres, as for 

 impressions carried upwards to them by the different nerves 

 which preserve their connection with the organs of the 

 various senses. 



STRUCTURE AND PHYSIOLOGY OF THE CEREBELLUM. 



The cerebellum (7, 8, 9, 10, fig. 147) is composed of an 

 elongated central portion called the vermiform processes, 

 and two hemispheres. Each hemisphere is connected with 

 its fellow, not only by means of the vermiform processes, 

 but also by a bundle of fibres called the middle cms or 

 peduncle (the latter forming the greater part of the pons 

 Varolii), while a superior cms with the valve of Vieussens, 

 connects it with the cerebrum (fig. 147, 5,) and an inferior 

 trus (formed by the prolonged restiform body) connects it 

 with the medulla oblongata (3, fig. 147). 



The cerebellum is composed of white and grey matter 

 like that of the cerebrum, but arranged after a different 

 fashion as shown in fig. 147. 



Besides the grey substances on the surface, however, 

 there is near the centre of the white substance of each 



