Coiupnisatorv Motions 449 



ciation with the other auditory organs and the fact that the three 

 canals of each side he in planes ahnost exactly at right angles 

 to one another; that is, in planes corresponding to the three 

 dimensions of space. It can be readily shown that the perception 

 of the direction of sounds is actually accomplished otherwise; 

 and this theory as to the function of these organs has been long 

 abandoned. 



In 1828 Flourens (i and 2) made the observation that, as a result 

 of cutting one of the membranous canals in a pigeon, the bird 

 moved about an axis at a right angle to the plane of the injured 

 canal; that is to say, the movement was in the plane of the divided 

 canal; the sense of hearing, however, was in nowise affected. The 

 disturbed movements were so much like those resulting from inju- 

 ries to the cerebellum that Flourens concluded that the canals were 

 concerned in the coordination of movements; but he made no 

 attempt to explain the method of their operation. 



In 1870 Goltz offered an explanation of the method of the work- 

 ing of the semicircular canals. According to this theory it is the 

 downward pressure of the endolymph on the various parts of the 

 sensitive lining of the membranous canal, according to the posi- 

 tion of the head, that gives rise to the corresponding sensations. 

 This theory has been called the "hydrostatic theory." 



A few years later, Breuer ('74, '75) and Mach ('75) proposed 

 hydrodynamic theories of the action of the canals. According 

 to Mach the sensations in the canals are aroused by variations in 

 the pressure of the endolymph in the ampullae, and the varia- 

 tions in pressure result from the streaming of the endolymph, 

 which is caused by movements of the head. According to Breuer 

 it is the movements of the endolymph, resulting from the move- 

 ments of the head, that arouse the corresponding sensations, 

 through their pressure on or movement of the lining hairs of the 

 canals. 



About the same time Crum-Brown ('74, I, 2 and 3) urged the 

 view that the movement or pressure of the perilymph was as much 

 concerned in the production of the sensation as the disturbance 

 of the endolymph; and he also pointed out that the canals operate 

 in pairs. 



