ORGANS OF SPECIAL SENSE. 359 



canal. It passes backward, downward, and outward, and is pro- 

 tected at its inferior extremity by a valve of mucous membrane 

 the valve of Hasner. 



The mucous lining is continuous with that of the sac, but 

 instead of having squamous epithelium it is ciliated in the duct. 



THE EAR. 



THE EAR the organ of hearing -is contained in the petrous 

 and mastoid portions of the temporal bone, and consists of three 

 divisions, external ear, middle ear or tympanum, and internal 

 ear or labyrinth: 



. f Auricle, or pinna, 



\ External auditory canal or meatus; 



f Membrana tympani, 



2. Midd,e ear or tympanum, \ Egf^ 



[_ Eustachian tube; 



f Vestibule, 



{Osseous portion, < Semicircular canals, 



I Cochlea; 

 f Utricle, 

 Membranous portion, ^^rcular canals, 

 [ Cochlea. 



The external ear includes two parts, the auricle and the 

 external auditory canal. 



AURICLE, OR PINNA. 



The external prominent portion is composed of cartilaginous 

 segments, connected together by ligaments and muscles richly 

 supplied with blood-vessels, nerves, and lymphatics, and covered 

 with skin. It presents the following elevations and depres- 

 sions : 



Fossa of the helix,, a depression between the helix and anti- 

 helix ; 



Fossa of the antiJielix, a depression above the bifurcation of 

 the antihelix; 



Tragus, the prominence in front of the concha, usually cov- 

 ered with hair ; 



Antitragus, a small, conical eminence behind the tragus, 

 from which it is separated by the incisura intertragica ; 



Lobule, the soft, rounded portion depending below the anti- 

 tragus ; 



