THE LABYRINTHINE SENSATIONS 



653 



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. 324). 

 The crista is composed of hair-cells with sustentacular cells between them. The fibres 

 of the vestibular nerve end in arborisations among the hair-cells, the hairs of which 





FIG. 324. End organ of vestibular nerve in ampulla of semicircular canal (' crista 



acustica '). 



project into the endolymph rilling 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 ampullsB. 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 

 movements of the head from side to side 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 those of his pupil Ewald, showed that these effects might last 

 .twelve to eighteen months, or be permanent, and must therefore be regarded 



