THE LABYRINTHINE SENSATIONS 605 



together three planes one horizontal and two vertical, the two latter being at righ 

 angles to one another (Fig. 312). The membranous canal lies within the osseous 

 canal, a considerable space intervening between the two canals. At one end the osseous 

 canal is dilated and the membranous canal undergoes a corresponding dilatation so as 

 to fill up the whole bony canal. In this dilatation, which is known as the ampulla, 

 we find the ending of a branch of the vestibular nerve in a special sense epithelium 

 forming the crista acustica (Fig. 313). The crista is composed of hair-cells with sus- 

 tentacular cells between them. The fibres of the vestibular nerve end in arborisations 



FIG. 313. End-organ of vestibular nerve in ampulla of semicircular canal (' crista 



acustica '). 



among the hair-cells, the hairs of which project into the endolymph filling the ampulla. 

 In the utricle and saccule we also find special sense-organs, known as the macula acustica, 

 the structure of which is very similar to that of the crista in the ampullae. Among the 

 hairs, however, of the macula is found a small concretion of carbonate of lime, the 

 otolith. 



The first accurate experimental investigation of the functions of these 

 different parts we owe to Flourens. This observer showed that, whereas 

 extirpation of the cochlea caused deafness, extirpation of the vestibule and 

 semicircular canals left the auditory sense intact, but caused marked dis- 

 orders of equilibration. That the peculiar arrangement of the semicircular 

 canals in the three planes of space was connected in some way with the 

 functions of these structures was also indicated by Flourens' observation that 

 destruction of the horizontal canals on each side gave' rise to continual 

 nodding movements of the head in the plane of the injured canals. By many 

 physiologists the results obtained by Flourens were ascribed to continued 

 irritation of the peripheral sense-organs or of the central parts of the brain in 

 consequence of the lesion. The accurate experiments of Goltz, and especially 



