THE ORGANS OF SPECIAL SENSE. 59 



tion is easily remedied. Nosebleed, though generally un- 

 important, may be serious in adults. 



The Mouth. The mouth is of great importance as an 

 entrance for fresh air to the lungs when the nasal passages 

 are for any reason impeded and as the resonant chamber 

 from which proceeds the voice, man's chief means of 

 communication with his fellows. Its chief value may be 

 said, however, to reside in the fact that it is the vestibule 

 of the alimentary canal. It is an ovoid cavity lined with 

 mucous membrane and is bounded in front by the lips, 

 at the sides by the cheeks, below by the floor and tongue, 



FIG. 19. The hyoid bone. (Toldt.) 



and above by the hard palate anteriorly and by the soft 

 palate posteriorly, the uvula depending from the latter 

 like a curtain between the mouth and the pharynx. 

 Shape is given to the mouth by the bones of the upper 

 and lower jaw and its -size is altered by the lowering and 

 raising of the latter, which is quite freely movable. 



At the back of the mouth, at the entrance to the phar- 

 ynx, are the anterior and posterior pillars of the fauces, 

 which contain muscular tissue, and between which on 

 either side are thick masses of lymphoid tissue, the tonsils. 

 The floor of the mouth is formed largely by the tongue, 

 which completely fills the space within the lower teeth. 



