SEMICIRCULAR CANALS AND THE VESTIBULE. 411 



hair cell are found masses of small crystals of calcium carbonate, 

 the otoliths or otoconia. In this respect the structure of the 

 macula differs strikingly from that of the crista. The position and 

 connections of the utriculus and sacculus lead at first naturally to 

 the supposition that they are stimulated by the sound waves of the 

 perilymph, and are, therefore, concerned in the function of hearing. 

 The accepted views regarding the functions of the cochlea in hearing 

 make this organ sufficient for all auditory purposes, and there is no 

 specific part of this process that need be attributed to the vestibu- 

 lar sacs. It was, indeed, at one time suggested that their structure 

 adapts them to respond especially to short and irregular vibrations, 

 but no cogent reasons or facts have been advanced to support this 

 view. The fact that the sacs are so closely connected with the 

 semicircular canals suggests rather that the functions of these organs 

 are similar and that like the canals, therefore, they influence the 

 contractions of the muscles and function as organs of equilibrium. 

 In recent years the view that has been most discussed is that ad- 

 vanced by Breuer, — namely, that these organs give us information 

 regarding the position of the head when at rest and when mak- 

 ing progressive — that is, non-rotary — movements, supplementing, 

 therefore, the functions of the semicircular canals on the supposition 

 that these latter act especially in movements of rotation. Or, as it 

 is sometimes expressed, the sacs form a static and the canals a dy- 

 namic organ of equilibrium. This plausible view has not been 

 supported by observations* made upon the cartilaginous fishes in 

 which the structures involved are accessible to direct experiment, 

 although such observations do give proof that the maculae take 

 part in controlling the equilibrium of the animal. We may assume 

 that the otoliths suffer a displacement when the head is moved 

 from one position to another and that this displacement serves to 

 put a stress or tension upon the hairs of the hair cells and thus gives 

 rise to stimuli varying with the amoimt or direction of the move- 

 ment. Maxwell reports that in the cartilaginous fishes the animal 

 shows compensatory movements of the eyes for rotations and 

 static changes in position when the ampullae of the semicircular 

 canals are destroyed, provided the macular apparatus is intact, 

 and similar responses when the otoliths are removed, provided the 

 ampullse are intact. These compensatory adjustments disappear, 

 however, if both organs are destroyed. It has also been shown 

 that direct displacement of the otoliths causes compensatory 

 movements of the eyes which vary with the direction of the 

 pressure. These experiments show that the maculse participate 

 with the ampullae in causing reflex compensatory adjustments for 

 changes in position of the head, but they give no indication of a 

 difference in function such as is assumed in Breuer's hypothesis. 



* Maxwell, "The Journal of General Physiology," 3, 157, 1920; see also 

 Lee, "American Journal of Physiology," 1, 128, 1898. 



