82 STUDIES IN PHYSIOLOGY 



The muscle fibers run through it in three directions, and by 

 their separate or combined action the free end of this organ 

 can be moved about at. will. When one examines the 

 mucous membrane on the upper surface of the tongue, one 

 sees elevations of different sizes, called pa-pil'lae (see p. 294). 

 Nerve fibers carry messages from the papillae to the brain, 

 and thus we become conscious of the senses of taste and 

 touch. 



Functions of the Tongue. The tongue has the following 

 uses : (1) it pushes the food between the teeth and so helps 

 in the process of mastication ; (2) it is the principal organ 

 of taste ; (3) as soon as the food is ready to be swallowed, 

 the tongue arches upward and forces the pasty mass back 

 into the throat ; (4) the tongue is likewise essential in speak- 

 ing. The so-called lingual (Latin lingua = tongue) conso- 

 nants, t, d, and n, are pronounced when the tongue touches 

 the roof of the mouth. 



4. THE SALIVARY GLANDS 



Position and Action of the Salivary Glands. In addition to 

 the mucus given out by the mucous membrane, the mouth 

 receives another secretion called sa-li'va. At the sight or 

 smell of tempting food, "the mouth waters." A sudden 

 fright or nervousness, on the other hand, stops the flow of 

 this secretion. Saliva is secreted by the salivary glands. 

 Two of these glands, the pa-rot'ids (Greek, meaning "beside 

 the ear"), are located near the back part of the lower jaw- 

 bone just beneath and in front of the ear. Any one who 

 has had the mumps can readily locate these organs, for 

 mumps is a disease in which the parotid glands swell. From 

 the parotid gland of each side a duct conveys saliva along 

 through the walls of the cheek. This duct opens at the 

 apex of a small elevation, easily felt with the tip of one's 

 tongue, on the inside of the cheek opposite the upper second 

 molar teeth (Fig. 28). 



