78 THE HUMAN BODY. 



mouth is closed they circumscribe its limits like an internal 

 wall. They are twenty in number in the child, and thirty-two 

 in the adult. They are divided into eight incisors, four canine, 

 and twenty molars. The last four molars are called the 

 "wisdom teeth." A tooth is composed of three distinct 

 parts: the pulp, the ivory, and the enamel. Vessels and 

 nerves penetrate the pulp, but do not go beyond; the ivory 

 which envelopes the pulp constitutes the root and the crown 

 of the teeth. That part of the tooth where the crown joins 

 the root is called the neck. This last is covered with a layer 

 of bony tissue. The crown commences at the neck, and is 

 overlaid with the enamel, a tissue very poor in animal sub- 

 stances, and almost inorganic. The teeth are not bones; 

 though their roots have an osseous covering, they do not 

 present either in their essential parts the ivory and the 

 enamel or in their mode of development and their physio- 

 logical conditions, any connection with the osseous system; 

 they are considered as analogous to the epidermic productions, 

 the hair, nails, &c., which they resemble in many respects. 



Palate. The palatine arch is formed, as we have already 

 seen, by the upper jaw-bones and the palatine bones. It is 

 circumscribed in front and on the sides by the upper teeth. 

 It is covered with a thick mucous membrane, very hard, and 

 presenting transverse ridges. Behind, it is continued by a 

 musculo-membranous partition, called the veil of the palate 

 the soft palate covered anteriorly by the mucous, buccal, 

 posteriorly by the pituitary membrane. Its inferior border 

 is free and floating, presenting on the median line an appen- 

 dage called the uvula. Each of its lateral borders forms 

 a continuation with the tongue and the pharynx by two 

 folds, which are called the pillars of the soft palate, and be- 

 tween which on either side lie the tonsils. In a state of 

 repose the soft palate closes the back part of the mouth; 

 but when raised prevents the food and drink, and the voice 

 also, from passing into the nasal fossae. 



The tongue is a fleshy body, symmetrical, longer than it is 

 broad, flattened from above downwards, thicker toward the 

 middle than at its extremities, larger behind than in front, 

 and rounded on the edges. The posterior extremity of the 



