No. I.] THE VERTEBRATE EAR. 249 



the same direction indifferently, whether the horizontal or verti- 

 cal canals were cut. 



Although there is a certain dependence of the disturbance on 

 the direction of the canal sectioned in the pendular movements 

 of the head on section of two canals, there are frequent enough 

 undeniable variations. It is especially to be noted that the 

 pendular motions of the head may be entirely absent, as happens 

 most frequently, and at the same time often, in section of the 

 posterior canal, and they may be replaced by others : the mal- 

 position of the head is such as usually only occurs after several 

 days. Hensen has likewise pointed out that when motion fol- 

 lows canal section it is apparently due to the current of escaping 

 lymph flowing on through the ear, which of course would cause 

 irritation of the sense organ belonging to the canal, and thus 

 give rise to the sensation of pain, the feeling of being wounded, 

 which is also sufficient to account for all the motions observed. 

 When one remembers in this connection that the malposition 

 of the head may persist for a month or two and then give way 

 to a return of the pendular motions, it is apparent that the latter 

 have their cause also in the central disturbances. This deduc- 

 tion finds weighty substantiation in the configuration of the 

 parts and in the very intimate connection between the brain 

 and the semicircular canals. In Pigeons, the aqiLCBductiis ves- 

 tibuli, after passing through the apertura aquaeductus vestibuli, 

 according to the investigations of Hasse and Boettcher, opens 

 into the subdural space. Consequently the endolymphatic fluid 

 is continuous with the cerebro-spinal liquid, as Schwalbe and 

 F. E. Weber have proven. In each operation of canal section 

 there is thus brought about a change within the cranial cavity 

 which has direct influence on the brain. Since the cranial 

 cavity is opened on canal section, the pressure conditions of the 

 brain are at once altered, owing to the escape of endolymphatic 

 fluid and cerebro-spinal liquid. The pressure is of course sud- 

 denly lowered, and Magendie has shown that the usual conse- 

 quences of tapping these liquids is the so-called " Taumel- 

 erscheinungen." 



Thus the primary symptoms are explained, which, so far as 

 motor disturbances of the body are concerned, are only different 

 in degree, as one or both sides are operated upon. The pendular 

 motions of the head are more difficult of explanation, following 



