ANIMAL DENTISTRY. 25 



tooth. Its fibers are continuous with the stroma of the 

 crusta petrosa and that of the alveolar wall, forming a firm 

 connecting medium betw^een the two. In the virgin tooth 

 it has all the characteristics of a membrane, but it soon loses 

 this feature and becomes confused with the crusta petrosa, 

 which tissue it develops. 



THE GUMS. 



The gums, or gingivae, may be considered in the sense 

 of a hypertrophy, either of the buccal mucous membrane or 

 of the alveolo-dental periosteum, to both of which they are 

 intimately connected. They consist of dense fibrous tissue, 

 the fibers of which intermingle with the alveolo-dental peri- 

 osteum and crusta petrosa, with the purpose of hermetically 

 sealing the alveolar cavities from external influences. 



BLOOD VESSELS. 



The blood supply of the teeth is derived from the su- 

 perior and inferior dental arteries, branches of the external 

 carotid. The superior dental is given ofif the internal maxil- 

 lary, passes into the superior dental foramen of the maxi!- 

 lary hiatus, through the superior dental canal as far as the 

 infra-orbita! foramen, along the roots of the third, second 

 and first molars, and then through the premaxilla to the ca- 

 nines and incisors. Along the course of the dental arcades 

 it gives off branches, for each tooth, which pass into the 

 pulp cavity through the apical foramina. The inferior den- 

 tal artery has the same general distribution via the inferior 

 dental canal. In addition to this principal blood supply teeth 

 receive nourishment from surrounding blood vessels by 

 way of the alveolo-dental periosteum to the extent of pre- 

 serving the integrity of the tooth should its principal supply 

 be interrupted. 



