60 



THE HUMAN BODY. 



inclosed by it on all sides, except for the oval and round 

 foramens on- its 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 bony labyrinth thus consti- 



Vc 



FIG. 164. 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 ; rpa, ampulla of 

 posterior vertical semicircular canal ; re, conjoined portion or the two vertical 

 canals. 



tuted, 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 perilympli; and the mem- 

 branous 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 differ- 

 ent aspects in Fig. 164. 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, communicating with the back of 

 the vestibule at each end, and dilated near one end to form 

 an ampulla (vpa, vaa, and ha). The horizontal 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 posterior parallel, to the median 

 antero-posfcerior vertical plane of the head. Their ampulltiry 

 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. 



