322 ALVEOLO-DENTAL-PERIOSTEUM. 



The gum is traced from the neck of the tooth into the al- 

 veolar cavity, as continuous with, and constituting the 

 alveolo-dental periosteum. In the infant state the gums 

 present on their superior edge a dense, white, cartilaginous 

 ridge, which becomes thinner and thinner as the period 

 of eruption approaches. The failure to undergo this thin- 

 ning process is the not unfrequent cause of great irritation 

 and even of convulsions in teething. In the tissue of the 

 gums, mucous follicles are found, which have been mistaken 

 for glands furnishing the tartar, and have hence been 

 called tartar glands. But it is now settled that the tartar 

 is simply a deposit of calcareous matter from the saliva. 



Alveolo-dental periosteum. This membrane is fibrous in 

 structure is attached to the necks of the teeth- lines the 

 alveolar cavities covers the roots is connected to the 

 blood-vessels and nerves, where they enter the apices of 

 the teeth, and is believed by Mr. Bell, to enter the cavities 

 of the teeth, lining their interior walls, and being contin- 

 uous with, or the same as that of the pulp. 



It has just been stated that this membrane is believed 

 to be continuous with that of the gums. Others think 

 that the sac containing the pulp, which consists of two 

 coats, after the eruption of the teeth, forms (especially the 

 outer coat) this alveolo-dental periosteum; while Mr. Bell, 

 on the other hand, believes that the sac is entirely ab- 

 sorbed, and that this membrane is the same as the perios- 

 teum, covering the superior and inferior maxillary bones, 

 continued into the alveolar cavities, and from thence re- 

 flected on the roots of the teeth. This membrane is 

 important in maintaining the teeth in their sockets. 



In tracing the mucous membrane from the gums, we 

 next find it covering the roof of the mouth, the soft palate, 

 the interior of the cheeks, the tongue, and thence follow 

 it into the pharynx. 



The mucous membrane, covering the roof of the mouth , 

 is characterized by the thickness of its epithelium, the 

 density of its chorion, its strong adhesion to the bone, its 

 whitish color; and the numerous orifices noticed in it, 



