220 



UNCONSCIOUS NERVOUS OPERATIONS 



solid layer of enamel, the hardest tissue found in the body. 



The neck is the narrowed portion just below the crown, 



surrounded by the gum. The 

 root (one or more) is the re- 

 mainder of the tooth, which is 

 secured to the socket of the 

 jaw by means of the perios- 

 teum, through which it derives 

 nourishment. A tooth is com- 

 posed of a hard, close material 

 called dentine, much like bone, 

 but with less animal matter. 

 This is molded round the cen- 

 tral pulp cavity, which contains 

 the tooth pulp a mass of loose 

 connective tissue, blood vessels, 

 nerves, and cells of different 

 shapes, one sort of which builds 

 the dentine. A layer of true 

 bone, called tooth cement, sur- 

 rounds the dentine of that part 

 of a tooth embedded in the gum, 

 as enamel caps the crown. 



310. The Tonsils. Between the arches of the soft palate 

 lies on each side a soft rounded body covered with mucous 

 membrane and containing many small glands which se- 

 crete mucus. They are called the tonsils (Fig. 108). 

 Their use is unknown except that they furnish some pro- 

 tection to the larynx and pharynx. Being sometimes 

 permanently enlarged and subject to frequent inflamma- 

 tion, they are occasionally removed by the surgeon with 

 apparent advantage to the patient. 



311. The Pharynx (Fig. 108) lies behind the soft palate. 



Fig. 109. - Diagram of the 

 structure of a tooth. 



