SENSE OF HEARING. 



599 



The pinna (Fig. 375) is composed of yellow fibrocartilage 

 covered by skin, although in some parts, as the lobule, the cartilage 

 is absent. It is attached to the meatus and other parts by liga- 

 ments and muscles. 



FIG. 374. Semidiagrammatic section through the right ear : G, external audi- 

 tory meatus ; T, membrana tympani ; P, tympanic cavity ; o, fenestra ovalis ; 

 r, fenestra rotunda ; B, semicircular canal ; S, cochlea ; Vt, scala vestibuli ; Pt, scala 

 tympani (Czermak). 



External Auditory Meatus. This canal, extending from the 

 pinna to the membrana tympani, is about 3.2 cm. in length, the 

 outer 1.3 cm. being of cartilage, except at the upper and back 



Fossa of helix. 

 Anthelix. 



Helix. 



Fossa of anthelix. 



Tragus. 

 Lobule. 



FIG. 375. External ear. 



part, where its place is taken by fibrous membrane. The inner 

 2 cm. is osseous. The entire canal is lined with skin, which in 

 the cartilaginous portion of the canal contains sebaceous and 

 perspiratory glands, their product being cerumen or ear-wax 

 (p. 417). The skin lining the meatus also contains hair-follicles. 



