CEREBRUM 201 



of tetanus toxin this condition is reversed, and that stimuli 

 which in normal conditions will cause flexion now cause powerful 

 extension, and hence co-ordinated movement is impossible. 



(c) In these motor areas the lesion must be extensive to cause 

 complete paralysis of any group of muscles. A limited lesion 

 may simply cause a loss of the finer movements. Thus, a monkey 

 with part of the middle portion of the Rolandic areas removed 

 may be able to move its arm and hand, but may be quite unable 

 to pick up objects from the floor of its cage. 



(d) The limits of these areas may be mapped out by the 

 character and distribution of the cells. The great feature is 

 the presence of very large pyramidal cells, the cells of Betz, in 

 the sixth layer of the cortex (fig. 95). These are confined to 

 the ascending frontal lobes. But in front of this is a region 

 stimulation of which gives rise to movements, and in which 

 the cell arrangement is much the same except that the cells 

 of Betz are absent. Well out in the frontal region is a 

 patch, stimulation of which leads to movements of the eyes, 

 and this region is directly connected by a strong band of fibres 

 with the occipital lobe and with the cerebellum. It is present 

 only in animals which employ binocular vision. It has been 

 suggested that this intermedio-precentral region is specially 

 connected with the finer and more highly co-ordinated muscular 

 movements, such as those of the eyes and of the mouth in 

 speech. 



