122 HUMAN PHYSIOLOGY 



who does not give the horses the power of doing 

 their work, but controls their movements so as to 

 impart a regular motion to the vehicle. It is natural 

 that in disease of the cerebellum irregularity of 

 muscular movements should be noted as a prominent 

 sympton. 



THE CENTRAL GANGLIA. Buried deeply down 

 below the upper brain in the centre of the organ we 

 find certain masses of nerve cells constituting the 

 central ganglia. The function of these parts along 

 with certain other and associated regions in the brain 

 have not been clearly determined. The nearest 

 approach which can be made to an explanation of 

 their use is that of assuming that they act as deputies 

 of the upper brain and stand to the latter structure 

 in the relation which private secretaries occupy to 

 their employer. One of these central ganglia is 

 known as the corpus striatum, the other being called 

 the optic thalamus. It is believed that the former is 

 a kind of "brain clearing house" through which 

 motor messages are assorted and parcelled out when 

 proceeding from the cerebrum to the body. The 

 neighbour mass, constituting the optic thalamus, may 

 it is supposed act as " a receiving house," wherein 

 messages from the body passing to the cerebrum are 

 received and in some fashion or other fitted for 

 appreciation by the cells of the upper brain itself. 

 It is highly probable that the central ganglia may, 

 under certain conditions, act independently of the 

 cerebrum itself. In persons who are hypnotised or 

 mesmerised, the faculties of the cerebrum may be 

 supposed to be switched off for the time being, 

 leaving the central ganglia largely to carry on the 

 parody of conscious life represented in the mesmeric 

 state. 



