816 



DISSECTION OF TRE EAR. 



termination 

 by five 

 openings ; 

 one end 

 dilated ; 



form and 

 size ; 



they are 

 named 



superior 

 vertical, 



posterior 

 vertical, 



the ampulla, while 

 is joined with the 



Fibrous 

 membrane 

 lines the 

 labyrinth, 



and contains 

 a fluid. 



Cochlea : 



dissection 

 for it in dry 



the contiguous ends of two are blended together so as to give onb 

 five openings into that cavity. Each is marked by one dilate 

 extremity, called the ampulla. When a^ube is cut across it is not 

 circular, but is compressed laterally, and measures about ^\th of 

 an inch, though in the ampulla the size is as large again. 



From a difference in the direction of the tubes, they have been 

 named superior vertical, posterior vertical, and horizontal. 



The superior vertical canal (a) crosses the upper border of the 

 petrous part of the temporal bone, and forms a projection on the 



surface. Its outer end is 

 marked by 

 the inner 

 following. 



The posterior vertical canal (6) 

 is directed backwards from its 

 junction with the preceding 

 towards the posterior surface of 

 the temporal bone ; it is the 

 longest of all, and has its 

 ampulla at the lower end. 



The horizontal canal (c) has 

 separate apertures, and is the 

 shortest of the three. Deeper 

 in position than the superior 

 vertical, it lies in the substance 

 of the bone nearly on a level 

 with the fenestra ovalis ; its 

 dilated end is at the outer 

 side close above that aperture. 



Lining membrane of the osseous 

 labyrinth. A thin fibrous peri- 

 osteal membrane lines the vesti- 

 bule and the semicircular canals, 

 and is continuous with the 

 fibrous process in the aqueduct 

 of the vestibule. On the outer 

 wall of the cavity it stretches 



over the fenestra ovalis ; and in front it is prolonged into the cochlea 

 through the aperture of the scali vestibuli (fig. 301, g). The space 

 between the periosteum and the membranous labyrinth is occupied 

 by a thin fluid liquor Cotunnii or perilymph, which also fills the 

 scalse of the cochlea. 



COCHLEA. This part of the osseous labyrinth has a position 

 anterior to the vestibule, and has received its name from its 

 resemblance to a spiral shell. 



Dissection. To obtain a view of the cochlea it will be needful to 

 cut or file away the bone between the promontory of the tympanum 

 and the internal auditory canal on the preparation before used for 

 displaying the vestibule ; or this section may be made on another 

 temporal bone in which the semicircular canals are not laid bare. 



FIG. 302. REPRESENTATION OF THE 

 SEMICIRCULAR CANALS, ENLARGED. 



a. Upper vertical. 



b. Posterior vertical, and 



c. Horizontal canal. 



d. Common opening of the two 

 vertical canals. 



e. Part of the vestibular cavity. 



/". Opening of the aqueduct of the 

 vestibule. 



