THE BRAIN 113 



the mid-plane to the other while passing through. This 

 has to do with a prominent and curious truth that the 

 right side of the cerebrum sustains relations chiefly with 

 the left side of the body and vice versa. 



The limited portion of the brain-stem which inter- 

 venes between the medulla and the cerebrum is of 

 interest to us as containing way-stations on the paths 

 from the eyes and the ears to the higher centers. This 

 part of the brain is also known to preside over the 

 muscles which rotate the eyeballs, change the visual 

 focus for different distances, and alter the size of the 

 pupils. 



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. 



