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 ampullae of the canals, in 

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

 asustica) projecting into the lumen (Fig. 178s) ; (2) a large macula 

 acustica in the utriculus : this is continued into the recessus utricuJi 



FIG. 179. DIAGRAM OF THE ENTIRE AUDITORY ORGAN OF MAN. 



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

 Mt, tympanic membrane. 



Middle Ear. Ct, Ct, typmanic cavity ; O 1 , wall of same ;4p sound-conducting 

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

 the rod marked t corresponds to the stapes, which closes up the feuestra 

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

 pharynx ; 0", its wall. 



Internal Ear, with the greater part of the bony labyrinth (KL, KL 1 ) removed. 

 S, sacculus ; a, b, the two vertical canals, one of which (b) is shown cut 

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

 rinths respectively ; S.e, D.e, saccus and ductus endolymphaticus ; the latter 

 bifurcates at 2 ; Op, cavum perilymphaticum ; Cr, canalis reunions ; Con, 

 membranous cochlea, which gives rise to a blind sac at -f- ; Con 1 , bony cochlea ; 

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

 at the cupula terminalis (Ct) ; D.p, ductus perilymphaticus, which arises 

 from the scala tympani at d, and opens at D.p 1 . 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 ncglccta, 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 



