THE EAR 387 



THE EAR 



The ear is divided into the external ear, the middle ear, or 

 tympanum, and the internal ear, or labyrinth. 



The external ear, the projecting part, or pinna, and the 

 external auditory canal and meatus. The pinna or auricle is 

 ovoid in outline, concave externally, and facing outward and 

 somewhat forward, presenting eminences and depressions 

 to which various names have been given. Thus, the most 

 external ridge is the helix; parallel and internal to this is the 

 antihelix, a ridge which divides above to enclose the fossa of 

 the antihelix; between these two ridges is the fossa of the helix 

 (fossa scaphoidea); in front of the antihelix is a deep depres- 

 sion, the concha, which presents above and in front the com- 

 mencement of the helix; in front of the concha is a small process, 

 the tragus, which points backward; and behind this is the 

 antitragus, a deep notch, the incisura intertragica, separating 

 the two; and lastly, below these is the lobule. 



The pinna consists of a plate of yellow fibrocartilage covered 

 by skin and some adipose tissue. It enters also into the forma 

 tion of the external meatus, being attached to the external 

 auditory meatus of the temporal bone. The lobule contains 

 only fat and strong fibrous tissue. 



The external auditory canal is lj inches long, and runs from 

 the concha to the membrana tympani. It is directed obliquely 

 forward, inward, and downward, and presents an eminence 

 in the floor of the osseous part, which makes the direction of 

 the canal at first upward, then downward. It is narrowest 

 at its middle. Its floor is longer than the roof, on account of 

 the oblique position of the membrana tympani. It opens 

 externally by means of the external auditory meatus. 



The middle ear, or tympanum, is a cavity in the petrous portion 

 of the temporal bone, extending from the membrana tympani 

 to the outer wall of the labyrinth. Its width varies from y 1 ^ 

 to J inch. It contains the ossicles of the ear, with their liga- 

 ments and muscles, and certain nerves. It is filled with air, 

 and communicates by means of the Eustachian tube with the 

 pharynx. 



The roof of the tympanum is formed of very thin bone, which 

 separates it from the cranial cavity. The floor is also of bone 



