202 SPECIAL ANATOMY. 



3. The nucleus, germ of the tooth, nucleus s. pulpa dentis, lies in the cavity 

 of the tooth, cavum dentis, the shape of it being determined by that of the 

 cavity; it is a reddish body, consisting of uniting tissue, capillary vessels and 

 nerves, surrounded by a thin and very sensitive membrane. The arteries 

 come from Art. maxillar. internet. (Jlrtt. alveolar, anter., poster., and infer.) the 

 veins open into Ven. facialis ant. and post. the nerves are branches of ram. 

 maxillar. super, and inferior (N. alveolar, ant., poster, and inferior). 



432. The tissue of the gums, gingiva (ofaov), thicker and 

 more firm than the mucous membrane of the mouth, the continu- 

 ation of which it is, covers the alveolar processes of the jaws, 

 and is connected with the periosteum by a very vascular, loose 

 uniting tissue. It turns over the free edge of the alveolus for 

 about a line broad, and then passes into the periosteum of the 

 alveoli. It is provided with the glandul. tartaricae, mucous 

 glands, which deposit the so-called tartar; little sensitive when 

 cut, more when pressed; becomes hard like cartilage after the 

 teeth have fallen out, when it covers over the alveoli. Arteries : 

 coronar. super., submental., sublingual. Nerves: from n. 

 quintus. 



433. Development of the Teeth. 



a. Before their eruption. The jaws of a two to three months' foetus pre 

 sent a broad and deep fossa, which is divided by thin septa into cells, and 

 closed upon the free border by a whitish and firm fibrous tissue (dental car- 

 tilage). 



At the time when the dental sacculi form, prolongations of the dental car- 

 tilage go to the floor of each cell, line it from without, and leave a small 

 opening, only, for the entrance of the vessels and nerves. 



The dental sacculi, folliculi dentium, are closed membranes, filled with a 

 reddish, viscous fluid, four of which appear in the middle of the third month, 

 and six in the fourth month, in each jaw. 



The tooth germ, pulpa dentis, elevates itself at first in the fourth month, 

 from the flood of the sacculus, as a papilla-shaped body, the thin pedicle of 

 which forms the dental vessels and nerves, increases by degrees into the sac- 

 culus, it becomes the nucleus about which the tooth (the crown first) forms. 

 In the fifth month ossification commences, that is to say, thin elastic discs of 

 dentine are deposited upon the surface of the pulpa, and indeed, so many as 

 the tooth at a later period is said to have tubercles. At a later period they 

 coalesce and become strengthened by new discs annexed to them from within. 

 But the enamel is not deposited from the pulpa, nor even from the reddish 

 fluid which washes round it, but from the lamina of the dental sacculus turned 

 towards the cell, and, indeed, from an enlargement at the top of the crown 

 to which last it is applied, at first (even in the mature foetus) as a soft and 

 moist mass. 



In the fifth month the central, then the external, incisor teeth form and 

 become ossified; in the sixth month, the first molar, the canine, the second 

 molar teeth. 



b. Eruption of the (milk) teeth, dentition, eruptio dentium, dentitio prima. 

 When after the birth of the child the roots of the teeth have reached the 

 floor of the dental cells, the gum, in consequence of their farther growth, is 

 pressed upon, inflames, and thence becomes perforated. 



