THE TEETH 



171 



Structure of a Tooth. — ^The crown of a tooth contains a central 

 cavit}', called the pulp cavity, which is occupied by the dental pulp. 



The shape of the pulp cavity corresponds with that of the crown, 

 and it extends into the root, and as man}^ fangs as compose it, 

 terminating in a small opening on the apex of the fang. The 

 cavity also extends for a little into the cusps of the bicuspids and 

 molars, and in the incisors it is continued into each angle of the 

 crown. The wall of the cavity presents a number of openings, 

 which lead into the dentinal tubules. The dental pulp is composed 

 of a matrix of connective tissue, containing bloodvessels, nerves. 



Fig. 95. — Section of the Fang of 

 A Tooth. 



I, Cement; 2, Granular Layer of 

 Purkinje; 3. Dentinal Tubule». 



Fig. 96. — Enamel Prisms. 



A. Four prisms (Longitudinal View) ; 

 B, Surface of the Enamel. 



cells, and fibres, which latter seem to be processes of the cells. It 

 is destitute of lymphatics. The cells are scattered throughout the 

 matrix, and at the surface of the pulp they form a continuous 

 layer, being there known as the odontoblasts. This layer is some- 

 times spoken of as the memhrana eboris. The pulp is very vascular 

 and sensitive, its vessels and nerves reaching it through the minute 

 openings at the apices of the fangs. 



The substance of the tooth is formed of three tissues, namely, 

 ivory or dentine, enamel, and cement or crusta petrosa. The 



