HUMAN STRUCTURE AND LIFE-ACTIVITIES 467 



nective tissue, blood-vessels, and nerves. This is the so- 

 called pulp. The pulp-cavity extends down into each of 

 the roots of the tooth, and at the tip of a root is a small 

 opening through which nerves and blood-vessels enter, 

 The hard outer part of a tooth consists of the enamel, and the 

 main bulk is dentine, a kind of ivory. The roots of the 

 tooth, which are buried in holes or sockets of the jaw-bone, 

 are covered with a thin layer of bony substance, called 

 cement. 



387. The Tongue. Examine with a hand-mirror. The 

 elevations on the upper surface are papilke, and nerve- 

 fibers connect these with the brain. Their function is 

 that of taste and touch. The tongue is chiefly muscular 

 tissue, the muscle-fibers extending longitudinally, trans- 

 versely, and perpendicularly. Can you think of any relation 

 between such arrangements of the fibers and the possible 

 movements of the tongue ? 



388. Salivary Glands. The epithelium which lines 

 the mouth secretes a limited amount of thick fluid known as 

 mucus, hence it is called a mucous membrane. But most 

 of the fluid in the mouth is saliva from three pairs of salivary 

 glands. On either side of the head a gland lies beneath and 

 in front of the ear. These are the parotid (meaning beside the 

 ear) glands, and a disease affecting them is called parotitis * 

 or mumps. A duct from each parotid gland opens into the 

 mouth-cavity on a little elevation on the inside of the cheek 

 near the grinding teeth. The elevation can be seen by 

 using a mirror and holding the cheek away from the jaw. 

 The two other pairs of salivary glands are placed among the 

 the muscles beneath the tongue, and their ducts open into 



* Notice that the ending itis added to the name of the organ (parotid) 

 means inflammation or disease of the organ. Likewise, there are in common 

 use such words as appendicitis (inflammation of the appendix of the intestines), 

 gastritis (of the stomach), laryngitis (of the larynx), tonsilitis (of the tonsils), 

 and many other diseases designated by adding itis to the name of the organ 

 involved. 



