THE ORGAN OF HEARING. 



numerous in the vicinity of the pharyngeal opening (Riidinger, 72, 

 2). The cartilage of the Eustachian tube is in part yellow elastic^ 

 in part hyaline, and in certain portions presents the appearance of 

 white fibre-cartilage. 



C THE INTERNAL EAR, 



The internal ear consists of an osseous and a membranous por- 

 tion, the osseous and the membranous labyrinths ; the latter is con- 

 tained within the former, and, although smaller, presents the same 



Superior semicircular canal. 



Horizontal semi- 

 circular canal. 

 Posterior semi- 

 circular canal. 



Ampulla. 



^^ ^^ ^~ " Bony cochlea. 



Vestibule. Fenestra rotunda. 



Fig. 368. Right bony labyrinth, viewed from outer side : The figure represents the 

 appearance produced by removing the petrous portion of the temporal bone down to the 

 denser layer immediately surrounding the labyrinth (from Quain, after Sommering). 



general shape. The two structures are separated by a lymph-space 

 containing the perilymph. 



In the bony labyrinth we recognize a central portion of ovoid 

 shape, known as the vestibule, the outer wall of which forms the 

 inner wall of the tympanum and presents two openings, the fenestra 

 ovalis and the fenestra rotunda, separated by a ridge known as the 

 promontory. This ridge becomes continuous with the lower portion 

 of the bony cochlea, anterior and mesial to the vestibule and having 

 the shape of a blunt cone. From the posterior portion of the ves- 

 tibule arise three semicircular canals, known respectively as the 

 external or horizontal semicircular canal, the anterior superior vertical, 

 and the posterior inferior vertical semicircular canals. The canals 

 communicate with the vestibule by means of five openings, the 

 superior contiguous portions of the anterior and posterior canals 

 uniting to form the canalis communis before reaching the vestibule. 

 The three canals present near their origin from the vestibule enlarge- 

 ments known as the osseous ampullae. The osseous labyrinth is 

 lined throughout by a thin -layer of periosteum, covered by a layer 

 of endothelial cells. 



