SECT. I37.] 



THE TEETH. 



239 



of a canal (canalis dentalis), even extends into the fangs, and ter- 

 minates at the apex of each with a fine, usually simple, rarely 

 double (Havers, Raschkow) aperture. To the soft parts belong;, 

 first, the gum (gingiva), a hard substance, composed of the mucous 

 membrane and the periosteum of the jaws, which surrounds the 

 lower half of the crown or the neck of the tooth, collum ; secondly, 



A. 



Fig. 119. 



B. 



' 



Unman molar tooth; magnified about five times. A. a longitudinal, B. a transverse 

 ,1 11. i7. Enamel ; 6. pulp-cavity; c. cement ; d. dentine, with the canalieuli. 



the periosteum of the alveolar cavity, which connects the tootli 

 very firmly with the alveolus ; lastly, the dental pulp (pulp a dentis), 

 a soft substance rich in vessels and nerves, which fills the cavity of 

 the tooth, and which is connected by the aperture or apertures in 

 the root with the above-mentioned periosteum. 



The proper tooth (fig. 119) consists of three different tissues: 1. 

 the dentine, which constitutes the chief portion of the tooth, and 

 determines its general form ; 2. the enamel, which forms a tolerably 

 thick covering upon the crown; and 3. the cement, which covers 

 the fang externally. 



§ 137. The dentine, ivory, substantia eburnea, ebur (fig. 119, d), 

 is yellowish-white in aspect, and in thin sections of fresh tooth, 



