58 SPECIAL HISTOLOGY. 



§ 141. 



The soft parts of the teeth are : the periosteum of the alveolus, 

 the dental pulp, and the gum. The periosteum of the alveolus 

 is very intimately connected with the fangs of the tooth, and 

 has the same structure as any other periosteum, except that it 

 is softer, contains no elastic element and possesses an abundant 

 nervous network, containing many thick fibres. 



The dental pulp — the remains of the foetal dental papilla — 

 arises from the periosteum at the bottom of the alveolus, enters 

 the fangs, and, as a continuous, soft, reddish, very vascular and 

 nervous substance, fills their canals and the pulp cavity in such 

 a manner as to be everywhere in close adherence to the inner 

 surface of the dentine. The pulp consists of an indistinctly 

 fibrous connective tissue, totally destitute of the elastic element, 

 but containing many dispersed, round and elongated nuclei ; and 

 except that it occasionally contains narrow bundles, almost like 

 imperfect foetal connective tissue. A fluid may be expressed 

 from it which, like mucus, is coagulated by acetic acid and is 

 not dissolved in an excess ; and, similarly, the entire pulp is ren- 

 dered whitish by acetic acid, never becoming transparent like 

 perfect connective tissue. This substance constitutes the prin- 

 cipal mass of the pulp, so far as the vessels and nerves extend ; 

 but upon its surface we find, immediately beneath a delicate 

 structureless membrane, a layer of 002 — 0-04'" thick, composed 

 of many series of cells, 0-012'" long, 0-002 — 0-003'" broad, 

 cylindrical or pointed at one end, with long narrow nucleolated 

 nuclei of 0005"', arranged perpendicularly to the surface of 

 the pulp like a cylinder epithelium. More internally these 

 regular series are no longer recognisable, but the cells, without 

 losing their close radial arrangement, are more intermixed, and 

 pass, finally, by shorter and rounder cells, without any sharp 

 lines of demarcation, into the vascular tissue of the pulp. 

 These cells correspond with the formative cells of the dentine, 

 to be described presently, and they afford the materials for the 

 deposits of dentine upon the walls of the pulp cavity, which 

 take place even in the adult. 



The vessels of the pulp are excessively numerous, whence its 

 red colour. 3 — 10 small arteries enter each pulp of a simple 

 tooth, and ultimately form, as well in its interior as upon its 



