STRUCTURE OF THE TEETH. 375 



2. The dental pulp rises from the periosteum at the bottom of the 

 alveolus, enters the fang, and fills the cavity of the tooth, and the 

 dentinal canals ; being everywhere in close adherence to the inner 

 surface of the dentine. It is a reddish, soft, very vascular and nerv- 

 ous substance; and consists of mere rudimentary collagenous tissue, 

 inclosing many dispersed, round, and elongated nuclei, and a fluid 

 substance, with the vessels and nerves. It is invested externally by 

 a basement-membrane, underneath which is a layer g^ to -jj^ of 

 an inch thick, composed of many series of cells, y^^ of an inch 

 long, and ^^ of an inch broad, arranged perpendicularly to the 

 surface of the pulp like a conoidal epithelium the formative cells 

 of the dentine, to be described further on. 



The vessels of the pulp are very numerous. Three to ten small 

 arteries enter the pulp of a simple tooth, and form both internally 

 and upon its surface a loose plexus of capillaries, 3-^3 to ^^^ of 

 an inch in diameter. There are no lymphatic vessels. (Kolliker.) 



The nerves of the pulp are extremely abundant. Into every fang 

 enters a large trunk ( ? J w to 3 J n of an inch), and six or more fine 

 branches (of yJ^ to gj^ of an inch), containing fibres of T2 J UT j to 

 Was f an inch. Kolliker inclines to the opinion that they ter- 

 minate in loops ; but this is not yet demonstrated. 



3. The gum (gingiva) is the portion of the mucous membrane of 

 the mouth uniting the necks of the teeth and the alveolar margins 

 of the jaw-bones. It is pale red, and rather soft, though feeling firm 

 because resting on the bone and teeth. Upon the teeth it is J to 

 JLJ line thick, and has papillae of s ! to ^ of an inch long in old 

 people even y 1 ? of an inch. Like the papillae filiformes of the tongue, 

 they are covered with secondary papillae, and a conoidal epithelium, 

 which between the papillae is ? J n to , J^ of an inch thick. Some- 

 times on its upper portions there are rounded depressions in it, y 1 ^ 

 to J of an inch in diameter, with cells more cornified, and which 

 may be mistaken for glands. 



4. The periosteum of the alveolus is very intimately connected 

 with the fangs of the teeth, having the same structure as any other 

 periosteum, except that it is softer, contains no elastic tissue, and 

 possesses an abundant nervous network containing many of the 

 large nerve-fibres. 



Properties and Uses of the Teeth. 



The principal function of the teeth, viz. as masticatory organs, 

 is well understood. They are also subservient to speech. 



