THE INTERNAL EAR IN VERTEBRATES 577 



transversely by an upstanding ridge of sensory epithelium— 

 the canals and sensory ridges being so set that each lies 

 approximately in one of the three planes of space. 



Upon the walls of the saccular chambers are three sensory 

 areas (fig. 2, dotted areas in Rec. utr., Sacculus and Lagena) 

 each covered by an otolith or mass of calcareous matter and 

 stated to lie, like the sense organs of the semicircular canals, 

 approximately in the three planes of space. 



post: canal. 



MACULA? 



>ACC EMDOL.YM: 



AMT= CANAU 



ANT: AMP- 



REG: UTR'. 



CAN OTR-8ACC 



d 



o 



2 



u 

 a 

 o 



cC 



< 



a. 



d 



o 



c* 

 U 

 b. 



or 

 < 



a. 



V 



POST N TRUNK 



A.NT N TKUN K. 



Fig. 2. — A schematic left endolymph labyrinth seen from the mesial aspect, showing 

 all the chief structures ever found in this organ. 



The nerve endings are dotted. The whole labyrinth, except the pars basilaris, constitutes the equilibrating 

 labyrinth (vestibular of man). The recessus utriculi, sacculus and lagena contain the three otolith 

 organs. The sense organ of the pars basilaris {mac. das.) constitutes the organ of Corti. 



There are thus in the typical vestibular labyrinth two sets 

 of three sense organs so arranged that the members of each 

 set are aligned with some sort of accuracy in the three planes 

 of space — an arrangement approximating to that theoretically 

 the best for response to movements in any direction. 



And as a matter of fact there is a mass of experimental 

 evidence from 1828 onwards 1 to show that these sense organs 

 are concerned primarily in response to changes in the position 



1 Flourens, Mem. Ac. R. Sci. hist. France, t. 9, 1828, p. 455. 



