TONGUE AND TEETH. 123 



of the tooth depend. It serves to hold the tooth in place, as well as 

 to manufacture the cementum. The cavity which contains the tooth 

 and is lined by the pericernentum is called the alveolus. The layer 

 produced by the pericementum and covering the root of the tooth 

 is the cementum. The corresponding layer upon the crown of the 

 tooth is the enamel. The enamel and cementum enclose the den- 

 tine, commonly called ivory. In the cavity of the tooth, which is 

 surrounded by the dentine, is the pulp. The blood and nerve supply 

 of the tooth is conveyed through an opening at the extremity of each 

 root. A single nerve fibre enters each tooth and its branches follow 

 the course of the blood-vessels. 



The enamel is derived from the epiderm ; the dentine and ce- 

 mentum. from the mesoderm. A tooth is developed from the dental 

 ridge, which forms the enamel organ, and from the dental papilla, 

 which consists of mesodermic connective tissue. The latter grows 

 up toward the enamel organ, so that the two are in contact. The 

 enamel organ produces the enamel, and the dental papilla produces 

 the dentine. 



OUTLINE OF THE TEETH. 



Dentine 



f Fibrous reticulum. 



Matrix ] 



\ Calcareous salts. 



Dentinal tubules. 



fDentinal sheaths. 



L Dentinal fibers. 

 Interglobular spaces. 

 Schreger's lines. 

 Lines of Salter. 



C Membrane of Nasmyth. 



Enamel < Enamel prisms. 



[ Stripes of Retzius. 



f Lamellae. 



Cementum J Lacunae. 



1 Canaliculi. 

 [ Corpuscles. 



