THE TEETH. 301 



Numerous small o-lands, called lalrial glands, are found beneath the 

 mucous membrane of the lips, around the opening- of the mouth. They 

 are situated between the mucous membrane and the orbicularis oris 

 muscle. They are compound racemose glands of a rounded form, the 

 largest of them not exceeding the size of a split pea ; and they open 

 into the mouth by distinct orifices. Small sebaceous glands also occur, 

 at least occasionally, on the part of the red border of the lips which is 

 seen when the mouth is closed. 



Between the buccinator muscle and the mucous membrane of the 

 cheek are the luccal glands, similar to the labial glands, but smaller. 

 Two or three glands, larger than the rest, found between the masseter 

 and buccinator muscles, and opening by separate ducts near the last 

 molar tooth, are called the molar glands. The secretion of these glands 

 is understood to be mucus ; whether it has any of the s])ecific properties 

 of saliva is not known. The duct of the parotid gland also opens upon 

 the inner surface of the cheek, opposite to the second upper molar tooth. 



Immediately within the lips and cheeks, are the drnfaJ arches, consist- 

 ing of the teeth, gnms, and alveolar borders of the maxillie. Tlie gums 

 (gingivfe) are composed of a dense connective tissue, cohering very 

 closely wnth the periosteum of the alveolar processes, and covered by a 

 red and highly vascular mucous membrane, which is smooth in its 

 general surface, but is beset with fine papillae in the immediate vicinity 

 of the teeth. The epithelium covering it is, like that of the mouth 

 generally, scaly and stratified, containing in the deeper layers numerous 

 cells marked with ridges and furrows, like those described in the 

 epidermis (p. 211). 



THE TEETH. 



In the human subject, as in mammalia generally, two sets of teeth 

 make their appearance in the course of life, of which the first comprehends 

 the fcmporarg, deciduous, or mdJc teeth, whilst the second is named the 

 permanent set. The temporary teeth are twenty in number, ten in 

 each jaw, and the permanent set consists of thirty-two, sixteen above 

 and sixteen below. 



Deficiencies in the number of teeth sometimes occiu', and, on the other hand, it is 

 frequently increased by one or more supernumerary teeth. These are usually 

 small, and simple, and although generally distinct, they are sometimes attached 

 to other teeth : they occur more freqiiently near the front than the hinder teeth, 

 and are more often met with in the upper than in the lower jaw. 



GENERAL CHARACTERS OF THE TEETH. 



A tooth consists of three portions, viz., one which projects above 

 the gums and is named the body or crown, another fixed in the alveolus 

 or socket, the root, consisting of the fang ov fangs — and a third, inter- 

 mediate between the other two, and, from being more or less con- 

 stricted, named the cervix or neck (fig. 201). The size and form 

 of each of these parts vary in the different kinds of teeth. 



The roots of the teeth are acciu*ately fitted to the alveoli of the jaws, 

 in which they are implanted. Each alveolus is lined by periosteum (fig. 

 201, 4), which also invests the contained tooth as high as the cervix. 

 This dental periosteum, sometimes named the periodontal membrane, is 

 said to be richly supplied with nerves. It is blended with the dense 



