PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 843 



by an extension of the periosteum lining the cochlea, on the one side, and the mucous 

 membrane lining the tympanic cavity, on the other. 



In the bony vestibule, occupying about two-thirds of its cavity, are two distinct sacs ; 

 a large, ovoid sac, the utricle, situated in the upper and posterior portion of the cavity, 

 and a smaller, rounded sac, the saccule, situated in its lower and anterior portion. The 



FIG. 2&1. Diagram of the labyrinth, vestibule, and semicircular canals. From a photograph, and somewhat 



reduced. , (Kudinger.) 



Upper figure: 1, utricle; 2, saccule; 8, 5, membranous cochlea; 4, canalis reunions ; 6, semicircular canals. 

 Lower figure: 1, utricle ; 2, saccule ; 3, 4, 6, ampullae ; 5, 7, 8, 9, semicircular canals ; 10, auditory nerve (partly dia- 

 grammatic) ; 1 1, 12, 13, 14, 15, distribution of the branches of the nerve to the vestibule and the semicircular canals ; 

 16, ganglioform enlargement. 



utricle communicates with the semicircular canals; and the saccule opens into the mem- 

 branous canal of the cochlea by the canalis reuniens. At a point in the utricle corre- 

 sponding to the entrance of a branch of the auditory nerve, is a round, whitish spot, called 

 the acoustic spot (macula acustica), containing otoliths, or otoconia, which are attached 

 to the inner surface of the membrane. A similar spot, containing otoliths, exists in the 

 saccule at the point of entrance of its nerve. Otoliths are also found in the ampullae of the 

 semicircular canals. These calcareous masses are composed of crystals of carbonate of lime, 

 which are hexagonal and pointed at their extremities. Nothing definite is known of the 

 function of these calcareous bodies, which exist in man. mammals, birds, and reptiles. 



The membranous semicircular canals occupy about one-third of the cavity of the bony 

 canals. They present little ovoid dilatations, called ampullae, corresponding to the ampul- 

 lary enlargements of the bony canals. 



The membrane of the cochlea, including the lining periosteum, occupies the spiral 

 canal of the cochlea, which it fills completely. Viewed externally, it appears as a single 



