FUNCTIONS OF THE BRAIN 939 



eyes and fins, and electrical stimulation of the auditory nerve 

 causes movements compounded of the separate movements obtained 

 by stimulation of the ampullae one by one. Lee concludes that the 

 semicircular canals are the sense-organs for dynamical equilibrium 

 (i.e.; equilibrium of an animal in motion), and the utricle and saccule 

 for statical equilibrium (i.e., equilibrium of an animal at rest). 



The evidence from all sources points strongly to the conclusion 

 that afferent impulses are actually set up in the fibres of the auditory 

 nerve, through the hair-cells, by alterations of pressure or by stream- 

 ing movements of the endolymph when the position of the head is 

 changed. Rotation of the head to the right may be supposed to 

 cause the endolymph in the right external canal, in virtue of its 

 inertia, to lag behind the movement, and to press upon the anterior 

 surface of the ampulla. The disorders of movement after lesions of 

 the canals may be explained as the result of the withdrawal of 

 certain of these afferent impulses, and the consequent overthrow of 



Pig. 377. A, Frog after Extirpation of the Left Labyrinth, showing the Difference 

 in the Posture of the Limbs on the Two Sides. B, the Same Frog after Section 

 of the Posterior Roots of the Second Pair of Spinal Nerves. The head and 

 vertebral column remain rotated toward the side of the lesion, but the legs are 

 now held symmetrically. 



that equipoise of excitation necessary for the maintenance of equi- 

 librium. An experiment of Kreidl on a crustacean (palaemon) has 

 made it probable that the otoliths by their weight may mechani- 

 cally affect the hair-cells, and so increase their sensitiveness to 

 changes of position. This animal has the peculiarity that in moult- 

 ing the inner lining of the otocysts, in which the otoliths lie and 

 which open to the exterior, are shed along with the otoliths. When 

 moulting is over, the animal by means of its claws conveys fine 

 sand grains into the otocysts, where they function as otoliths. 

 Kreidl placed the animal after moulting upon finely powdered iron, 



