320 



THE NERVOUS SYSTEM 



canal of the other. At one end of each canal is a dilata- 

 tion, where is situated a hair-structure resembUng those 

 of the utricle and saccule, but without otoUths. 



When the horizontal canals are destroyed on both sides 

 there follow continual movements of the head in the 

 horizontal plane, a condition which lasts a considerable 



Fig. 57. — End-organ in ampulla of semicircular canal (from Starling's 

 Principles of Physiology): sec, semicircular canal; h., hairs; 

 amp., ampulla. 



time. When the canals on one side are destroyed there 

 follows, in addition to disorders of equihbrium, considerable 

 loss of tone on the same side of the body. 



When in the bird the canals are destroyed on both 

 sides the animal loses all sense of equihbrium, and per- 

 forms violent and perpetual somersaults. After a pro- 

 longed period it recovers in some degree. This is owing 

 to the education of other senses, chiefly the eyes, for when 

 the partially recovered bird is bhndfolded it reverts to 



