THE SENSE OF HEARING 725- 



hght around a -vertical axis and in a horizontal plane the endolymph in the 

 tfght half of each horizontal or lateral canal will flow toward the ampulla, 

 ind in the left half away from the ampulla. If the head is rotated to the 

 left the reverse movements would arise. 



If the head is rotated backward around a horizontal axis the endolymph 

 will flow in both posterior vertical canals in the opposite direction, i.e., away 

 from the ampullae and if the head is rotated around the same axis forward, 

 the reverse movement takes place. If the head is rotated around an oblique 

 axis, the endolymph will flow in the superior vertical canal of one side away 

 from the ampulla and in the posterior vertical canal of the other side toward 

 the ampulla. Thus whatever the plane of rotation of the head may be, 

 there is always a flow of endolymph in the opposite direction, which 

 movement, or variation in pressure, becomes the effective stimulus. The nerve 

 impulses developed by this stimulation when transmitted to the brain evoke 

 more or less conscious sensations, which inform us as to the direction and the 

 extent of movement of the head and calls forth the action of the mechanism 

 by which the movement is regulated and controlled and the equilibrium of 

 the body maintained. 



