THE LABYRINTHINE SENSATIONS 681 



once that the incidence of the weight of the otoliths on the hairs of 

 the macula will vary according to the position of the head. Thus in 

 the diagram (Fig. 201, p. 450) in A (normal position) the chief weight 

 of the otolith falls on the hairs from b to c, whereas, when the head 

 has been rotated round a right angle so that the man, for instance, 

 is lying on his right side, the chief weight of the otoliths will fall on 

 the hairs from c to d. The nerve-endings stimulated by the weight 

 of the otoliths will therefore vary according to the position of the 

 head. The cerebellum and its associated structures represent a 

 mechanism for the regulation of the movements of the trunk as 

 a whole and the position of its centre of gravity in relation to the 

 position of the head. 



The beginning and ending of all movements of the head, or any 

 change in the rate at which it is moving, must cause a momentary 

 alteration of the incidence of pressure of the otoliths on the sensory 

 hairs. Any translatory movements of the head must therefore 

 excite a set of nerve fibres which will be constant for each direction. 

 We are therefore justified in ascribing to these organs the functions 

 possessed by the otolith organ throughout the animal kingdom, 

 viz. the transmission of impulses to the central nervous system 

 which are aroused by the position or movements of the head, and, 

 like the sensations from the muscles, regulate and govern any motor 

 reaction to a sensory stimulus. Of these afferent impulses a certain 

 proportion will arrive at the cerebral cortex, and in consciousness 

 will inform us of our position in space and of the direction and extent 

 of any movement, active or passive, of the head. 



