THE SENSE OF HEARING 407 



tongue also possesses the property of conveying 

 impulses which give rise to sensations of touch and 

 temperature, and these make the classification of 

 sensations of taste most difficult. However, the tastes 

 have been classified into four primary groups: bitter, 

 sweet, acid, or salt. The intensity of the sensation of 

 taste produced by any one of these groups, or a com- 

 bination of them, is dependent upon their concentra- 

 tion; and the extent of the sensation depends on the 

 area affected, or the number of taste-buds coming in 

 contact with them. 



THE ANATOMY AND PHYSIOLOGY OF THE 



STRUCTURES CONCERNED IN THE 



SENSE OF HEARING 



The Ear. The ear is divided into the external ear, 

 the middle ear or tympanum, and the internal ear or 

 labyrinth. 



The External Ear. This consists of 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. 



The pinna consists of a plate of yellow fibrocartilage 

 covered by skin and some adipose tissue. It enters 

 also into the formation of the external meatus, being 

 attached to the margins of the external auditory meatus 

 of the temporal bone. The lobule contains only fat 

 and strong fibrous tissue. 



The external auditory, canal is 1 J inches long (adult), 

 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 



