ORGANS OF DIGESTION. 107 



A gland is a tiny tube or collection of branching tubes which 

 remove certain materials from the blood and manufacture 

 them into a fluid useful to the body. 



THE MOUTH. 



The mouth is bounded craniad by the lips, laterally by 

 the cheeks, and dorsally by the palate, where the mucous 

 membrane lies in seven or eight transverse ridges or rugae, 

 and caudally depends from the palatine bones forming the 

 velum palati. To display the anatomy of the mouth, one 

 should remove the right half of the mandible. From 

 either side of the velum palati two folds of membrane di- 

 verge as they extend to the floor of the mouth at the root 

 of the tongue. The cranial fold is the anterior pillar and 

 the caudal one is the posterior pillar of the fauces (Fig. 

 56). The caudal portion of the mouth between these folds 

 is known as the fauces. It opens into the pharynx. On 

 either side of the tongue between the two pillars is a 

 crescentic depression holding a tonsil. In man, the tonsils 

 sometimes become inflamed and enlarged, giving rise to a 

 disease called tonsilitis. The tonsil is a compound lym- 

 phatic gland whose function is unknown. 



Folds of mucous membrane called frena bind the lips to 

 the gums which are composed of dense fibrous tissue in- 

 vesting the alveolar margins of the jaw-bones. The mucous 

 lining of the mouth contains many simple mucous glands 

 invisible to the naked eye. Those of the lips are called 

 labial, of the cheeks, buccal, and of the palate, palatine 

 glands. 



The tongue lying in the floor of the mouth is a muscular 

 mass composed of the geniohyoglossus, lingualis superfici- 

 alis superior and inferior, styloglossus, and hyoglossus mus- 

 cles. Caudally it is attached to the hyoid bone. Its invest- 



