190 



THE HUMAN BODY 



exterior, and certain apertures on its inner side by which blood- 

 vessels and branches of the auditory nerve enter; during life all 

 these are closed water-tight in one way or another. Lying in the 



FIG. 71. Casts of the bony labyrinth. A, left labyrinth seen from the outer 

 side; B, right labyrinth from the inner side; C, left labyrinth from above; Fc, round 

 foramen; Fv, oval foramen; h, horizontal semicircular canal; ha, its ampulla; 

 Vaa, ampulla of anterior vertical semicircular canal; Vpa, ampulla of posterior 

 vertical semicircular canal; Vc, conjoined portion of the two vertical canals. 



bony labyrinth thus constituted, are membranous parts, of the 

 same general form but smaller, so that between the two a space is 

 left; this is filled with a watery fluid, called the perilymph; and 

 the membranous internal ear is filled by a similar liquid, the endo- 

 lymph. 



The Bony Labyrinth. The bony labyrinth is described in three 

 portions, the vestibule, the semicircular canals, and the cochlea; 

 casts of its interior are represented from different aspects in 

 Fig. 71. The vestibule is the central part and has on its exterior 

 the oval foramen (Fv) into which the base of the stirrup-bone fits. 

 Behind the vestibule are three bony semicircular canals, com- 

 municating with the back of the vestibule at each end, and dilated 

 near one end to form an ampulla (Vpa, Vaa, and ha) . The horizon- 

 tal canal lies in the plane which its name implies, and has its am- 

 pulla at the front end. The two other canals lie vertically, the 

 anterior at right angles, and the posterior parallel, to the median 

 anteroposterior vertical plane of the head. Their ampullary ends 

 are turned forwards and open close together into the vestibule; 

 their posterior ends unite (Vc) and have a common vestibular 

 opening. 



The bony cochlea is a tube coiled on itself somewhat like a snail's 

 shell, and lying in front of the vestibule. 



The Membranous Labyrinth. The membranous vestibule, lying 



