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 ruge, 
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 fauccs. It opens into the pharynx. On 
either side of the tongue between the two pillars is a 
crescentic depression holdinga tonsil. In man, the tonsils 
sometimes become inflamed an:l enlarged, giving rise to a 
disease called tonsilitis. The tonsil is a compound lym- 
phatic gland whose function is urknown. 
Folds of mucous membrane callecefrena bind the lips to 
the gums which are composed of deasse fibrous tissue in- 
vesting the alveolar margins of the jaw-»ones. 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. Caudaily it is attached to the hyoid bone. Its invest- 
