522 ELEMENTARY PHYSIOLOGY less. 



Now experiment and observation in cases of disease have 

 shown quite conclusively that the one (jreat function of 

 the cerebellum is to play a most important part in the co- 

 ordination of the actions, nervous and muscular, by ^vhich 

 the inovements of the body are carried on. 



After the cerebullum has been completely removed, an 

 animal does not differ in any essential respect from its 

 normal condition as i-egards its intelligence or its special 

 senses, such as sight or hearing. But with regard to its 

 movements a great difference is observed in the absence 

 of the cerebellum ; all movements are now clumsily 

 executed — there is a want of orderliness or co-ordination. 

 This statement sums up our knowledge of the function of 

 the cerebellum. 



We do not know hoio the cerebellum works in thus 

 keeping an orderly grip over the mechanisms of move- 

 ment ; but we see how easily it may do so when we 

 consider its connections with the spinal cord and with the 

 rest of the brain. We saw (p. 494) that the cerebellum 

 as well as the cerebrum sends fibres which connect with 

 the motor neurons in the anterior horn and (p. 491) that 

 two large tracts of afferent fibres from the spinal cord 

 pass into the cerebellum, viz. the cerebellar tract by the 

 inferior peduncle and the ascending antero-lateral tract by 

 the superior peduncle. Moreover the cerebellum is 

 connected with that part of the bulb in which the posterior 

 colum7i ends. Thus it may be a recipient of a vast 

 number of afferent sensory impulses, which are so 

 essential for co-ordinated movement. But each half of 

 the cerebellum is further connected with the cortex of 

 the cerebral hemisphere of the opposite side in two ways, 

 firstly, by the fibres of its middle peduncle across the 

 pons Varolii, and secondly, and more directly, by fibres 

 in its superior peduncle (see p. .o06). And we shall see 

 that it is exactly in the cortex of the cerebral hemispheres 

 that impulses chiefly arise for the initiation of muscular 

 movements. 



