42 ORAL EQUIPMENTS. 



the " Dental Pulp," a soft and highly vascular and sensitive 

 body, which is the remnant of the soft Papilla from which the 

 tooth in embryo has been elaborated by the deposition of 

 lime salts in a definite direction. This process of develop- 

 ment I hope to explain and illustrate in Section III. 



The Pulp is the principal source of vitality to the tooth, 

 and to it proceed through the canals before indicated the 

 nerves and blood-vessels from the main trunks in the 

 substance of the jaw-bones, carrying to the tooth the nutritive 

 pabulum, and sensation. 



Next to the Pulp we perceive a hard and ivory-like 

 substance, the " Dentine," which makes up the principle bulk 

 of most teeth in all the Vertebrates. Ivory of commerce is 

 dentine from the teeth of the Elephant, and certain other 

 animals. It is the tough and force-resisting portion of a 

 tooth. 



External to this on the crown we see the " Enamel," 

 absent in the teeth of some vertebrates; a hard stone-like 

 substance, for resisting the wear and tear of mastications. 

 On the root the " Cementum " ; a substance which in its 

 histological characteristics is closely homologous to bone. 

 Into and through this ramify blood-vessels and nerves, which, 

 derived from the same source as those of the pulp, afford 

 however sufficient nourishment to a tooth to retain it in the 

 mouth in functional activity after the pulp has been destroyed 

 by any cause. These vessels and nerves run through into the 

 cementum from the investing membrane, which holds the 

 tooth in situ in the bony socket ; and which acts as a pad to 

 resist shocks in mastication. It is called, where it covers the 

 root, the perimentum or peridental membrane, and where it 

 covers the bony socket, the periosteum. It is really one tissue 

 differing in its different parts from the tooth toward the bone 

 in its histological elements. Each tooth socket is divided 

 from its neighbour by laminse of bone called the Alveoli ; 

 hence the name given to the bone in which the teeth are 

 implanted, the "Alveolar process." Overlying this is the 

 gum. 



Please bear in mind these various names, for in speaking 

 of the different classes of animals, I shall have many interest- 

 ing modifications of structure to advert to. 



I must now name the various teeth as we find them in a 

 normal human jaw, and then I think the ground will be 

 pretty well cleared for understanding the real subject-matter 

 of my paper. 



In the front we have in each jaw four "incisors" or 



