AUDITORY ORGAN 



223 



The sensory epithelium, to which the branches of the auditory 

 nerve are distributed, is situated in the following parts of the 

 membranous labyrinth : (1) the three ampullse of the canals, in 

 each of which the auditory cells are situated on a ridge {crista 

 aOTSi;^ca)_ projecting into the lumen (Fig. 178b) ; (2) a large macula 

 acvstica in the utriculus : this is continued into the recessus utriculi 



Fig. 179. — Diagkam of the Entire Auditory Orgax or Max. 



External Ear. — M, M, pinna ; Mae, external auditory meatus ; 0, wall of latter ; 

 Ml, tympanic membrane. 



Middle Ear. — Ct, C't, typmanio cavity; C^, wall of same ; i?^4p, sound-conducting 

 apparatus, indicated by a rod, representing the auditory ossicles, the end of 

 the rod marked + corresponds to the stapes, Avhich closes up the fenestra 

 ovalis ; M, fenestra rotunda ; Tb, Eustachian tube ; Tb^, its opening into the 

 pharynx ; 0", its wall. 



Internal Ear, with the greater part of the bony labyrinth {KL, KL^) removed. — 

 S, sacculiis ; a, b, the two vertical canals, one of which [b] is shown cut 

 through ; c, Co, commissure of tlie canals of the membranous and bony laby- 

 rinths respectively ; S.e, D.i', saccus and ductus endolymphatious ; the latter 

 bifurcates at ■ 2 ; Cp, cavum perilymphaticum ; Cr, canalis reuniens ; Con, 

 membranous cochlea, wliich gives rise to a blind sac at + ; (Jon^, bony cochlea ; 

 Sv and St, scala vestibuli and scala tympani, which at * pass into one another 

 at the cupula terminalis {Ct) ; D.2J, ductus perilymphatieus, which arises 

 from the scala tympani at d, and opens at I).p'. The horizontal canal is 

 seen between 2 and S. 



as well as into the sacculus and lagena, or rudiment of the cochlea, 

 which arises from the sacculus ; (3) the rudimentary macula 

 acustica neglccta, which in Fishes, Birds, and Reptiles is situated on 

 the floor of the utriculus close to the sacculo-utricular canal. In 

 Amphibians it lies on the inner side of the sacculus, and in 

 Mammals undergoes a gradual reduction and may even become 



