THE INTERNAL EAR. 



different aspects in Fig. 145. The vestibule is the central 

 part and has on its exterior the oval foramen (Fv) inta 

 which the base of the stirrup-bone fits. Behind the vestibule- 

 are three bony semicircular canals, communicating 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 ampulla at the front end. The two other canals 

 lie vertically, the anterior at right angles, and the pos- 

 terior parallel, to the median antero-posterior vertical plane 

 of the head. Their amp ullary 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 vesti- 

 bule, lying in the bony, consists of two sacs communicating 

 by a narrow aperture. 

 The posterior is called 

 the utriculus, and into 

 it the membranous 

 semicircular canals 

 open. The anterior, 

 called the sacculus, 

 communicates by a tube 

 with the membranous 

 cochlea. The mem- 

 branous semicircular 

 canals much resemble 

 the bony, and each ha& 

 an ampulla; in most 

 of their extent they are only united by a few irregular 

 connective-tissue bands with the periosteum lining the 

 bony canals; but in the ampulla one side of the mem- 

 branous tube is closely adherent to its bony protector; at 

 this point nerves enter the former. The relations of the 

 membranous to the bony cochlea are more complicated. A 

 section through this part of the auditory apparatus (Fig. 

 146) shows that its osseous portion consists of a tube 



FIG. 146. A section through the cochlea 

 in the line of its axis. 



