378 



THE TISSUES. 



to be double or triple. The development of the fang from the den- 

 tinal pulp is precisely like that of the dentine in the body just de- 

 scribed ; and this process elevates the latter through the gum, and 

 thus the eruption of the tooth takes place. The enamel, of course, 

 covers the body only, since the enamel-sac extended only over the 

 latter. 4. Finally, as the alveoli close around the necks of the teeth 

 during their eruption, and afterwards more completely around the 

 fangs, the vessels of the periosteum of the alveoli deposit a plasma 

 from which the cementum (tooth-bone) is formed; and which be- 

 comes adherent to the dentine, and forms a layer becoming thicker 

 as it approaches the apex of the fang, as before described (p. 374). 



The explanation of the minutiae, of this process requires a know- 

 ledge of the minute structure of the dentinal pulp, and the enamel- 

 sac and its contents. And the following statement is deemed the 

 most accurate, in its details, of the various accounts given by dif- 

 ferent authors: 



1. The dentinal pulp precisely resembles, in size and form, the 

 body of the tooth to be developed from it, consisting of an internal 

 portion rich in vessels, and an external portion which is entirely 



Fig. 239. 



A. Tooth-sac of the second incisor of an eight months foetus, seen on the broad surface, a. Dental 

 sac. b. Enamel-pulp, c. Enamel-membrane, d. Enamel, e. Dentine. /. Dentinal cells, h. Dental 

 pulp. i. Free edge of the enamel-organ. B. First incisor of the same embryo, seen on the narrow 

 surface ; letters as before, a. Dentinal cap in toto. fc. Nerves and vessels of the pulp. Magnified 

 7 diameters. (Kolliker.) 



