THE BRAIN 115 



The Cerebellum and Equilibrium. It has been said 

 that the cerebellum is a dorsal outgrowth from the 

 brain-stem. It can be cut away without interrupting 

 the direct lines by which impulses pass along the nervous 

 axis. When the brains of different animal species are 

 compared we find that no correspondence between the 

 size of the cerebellum and intelligence can be established 

 This part of the brain is particularly large in birds and 

 fishes. One thinks naturally of the remarkable loco- 

 motor powers of these types, the coordinated muscular 

 system of the fish that corresponds in number of ele- 

 ments with the elaborate skeleton and the equipment for 

 flying which so distinguishes the bird. There is in 

 fact no doubt that the cerebellum stands in some re- 

 lation to locomotion and balancing. 



When it has been removed from a pigeon the bird 

 presents a distressing picture. It seems quite as sensi- 

 tive as a normal bird and overcome by panic. It can- 

 not fly; if tossed into the air it falls fluttering helplessly 

 and throws itself about on the ground. It cannot even 

 keep its feet. No muscles appear to be paralyzed, but 

 there is a lamentable loss of the ability to use them in 

 groups for common ends. A bird that has undergone 

 this operation will injure itself if it is not restrained. 

 If it is carefully kept and tended it improves considerably, 

 but does not recover its original poise and control. 



A similar experiment has been made upon the dog. 

 With this animal also the first impression is of utter 

 failure to coordinate the movements. The dog rolls 

 and writhes as though convulsed with pain. Yet it is 

 probably not suffering unless from terror and bewilder- 

 ment. After a time there is a great degree of recovery 

 but there is a permanent unsteadiness, awkwardness, 

 and quick susceptibility to fatigue. On the whole 

 there seems to be no doubt that, while the earlier ex- 

 perimenters assigned the function of equilibration too 

 exclusively to the cerebellum, it does have to do with 



