FUNCTIONS OF THE BRAIN 



937 



are borne by some of the columnar cells, between which lie more 

 elongated fibre-like supporting cells. The hairs project into a mucus- 

 like mass, sometimes containing otoconia, or crystals of calcium car- 

 bonate. The ampullae, like the rest of the membranous labyrinth, is 

 filled with a watery fluid called endolymph. The utricle and saccule 

 have each a somewhat similar but broader elevation, the macula 

 acustica, covered with epithelium and hair-cells of the same character, 

 and the hairs project into a similar mass in which otoconia are con- 

 stantly present. In some animals, as fishes, the calcareous matter in 

 the utricle and saccule forms masses of considerable size (otoliths}. 

 Fibres of the auditory nerve end in arborizations around the bodies 

 of the hair-cells of the maculae and cristae acusticse. We have already 

 seen that it is the ventral or vestibular division of the nerve which is 

 especially related to the vestibule (p. 927). 



There is very strong evidence that the semicircular canals are con- 

 cerned, not in hearing, but in equilibration. A pigeon from which 

 the membranous canals have been removed still hears perfectly 

 well so long as the cochlea is intact, but exhibits the most profound 

 disturbance of equilibrium. If 

 the horizontal canal is destroyed 

 or divided, the pigeon moves its 

 head continually from side to side 

 around a vertical axis ; if the 

 superior canal is divided, the 

 head moves up and down around 

 a horizontal axis. The power of 

 co-ordination of movements is 

 diminished, but not to the same 

 extent in all kinds of animals. 

 Thrown into the air, the pigeon is 

 helpless ; it cannot fly ; but a goose 

 with divided semicircular canals 

 can still swim. The condition is 

 only temporary, even when the 

 injury involves the three canals 

 on one side; but if the canals on 



both sides are destroyed, recovery Fig. 376. Dog Twenty - two 

 is tardy, and often incomplete. 

 In mammals the loss of co-ordina- 



Months 



after Destruction of Right Labyrinth 

 (Wilson and Pike). 



tion is less than in birds, although at first the animal is unable to 

 walk properly, easily falls over to the injured side, and goes con- 

 tinually in a circle turning towards the side of the lesion. Move- 

 ments of the eyes, the direction of which depends on the canal 

 destroyed, take to a large extent the place of movements of 

 the head. Torsion of the head towards the side of the injury is, 

 however, pronounced and permanent (Wilson and Pike) (Fig. 376). 

 Speaking generally, the eyes are deviated to the side of the lesion, 

 and exhibit the phenomenon of nystagmus. 



