THE SENSE OF MOVEMENT DYNAMIC SENSE 



787 



Fig. 400. — Diagram to 

 Show the Position of the 

 Semicircular Canals To- 



It is 19 mm. in length and rises to a higher level than any other part of 

 the labyrinth, its location being indicated upon the upper surface of the 

 petrous portion of the temporal bone by an arched prominence. Its 

 ampulla is situated in front. The posterior or inferior canal (P) is also 

 placed nearly vertical at an angle of 45° to the mesial plane of the body 

 but in such a way that it inclines toward the superior canal at a right 

 angle. It measures 22 mm. in length and its 

 ampulla Ues at the back part of the vestibule. 

 A comparison of the planes of these canals 

 with those of the canals on the opposite side 

 shows immediately that the left anterior covers 

 the same plane as the right posterior, and the 

 right anterior that of the left posterior. It is 

 evident, therefore, that they supplement one 

 another. In this connection, attention should 

 also be called to the fact that the vestibular wTrd ONE^AjiroTHER' 

 division of the auditory nerve divides into two 



branches, namely, into the ramus utriculo-ampullaris and the ramus 

 sacculo-ampullaris. The former innervates the utricle and ampullae 

 of the superior and horizontal canals, and the latter, the saccule and 

 ampulla of the posterior canal. 



The Effects of Lesions of the Semicircular Canals. — The first 

 accurate investigations pertaining to the function of the semicircular 



canals, have been made by Flourens* 

 upon pigeons, these animals having 

 been selected for this purpose because 

 their labyrinth is more accessible to 

 operative procedures than that of 

 the mammals. It was found first of 

 all that the destruction of the vesti- 

 bule and adjoining semicircular canals 

 does not impair the sense of hearing, 

 but merely evokes disorders of equili- 

 bration, which, in accordance with 

 Goltz,2 are the result of an abolition 

 of function and not of a loss of stimu- 

 lation. Thus, it could easily be shown 

 that the unilateral destruction of the 

 canals renders the animal unable to 

 maintain its position. If it is made to 

 move, it sways and repeatedly tiunbles 

 The head remains tilted toward the 

 operated side and is even held in an inverted position. These symp- 

 toms disappear in the course of three or four weeks so that the animal 



1 Compt. rend., lii, 1828; also : Vulpian, Legons, sur la physiol. du syst. nerveux, 

 Paris, 1866. 



2 Pfluger's Archiv, iii, 1870, 172. 



Fig. 401. — Abnormal Posture of 

 Pigeon, in Which the Labyrinth had 

 BEEN Extirpated on One Side Five 

 Days Previously. (Ewald.) 



toward the side of the injury. 



