62 SPECIAL HISTOLOGY. 



of fetal life, and at the seventh, ossification has commenced in all 

 of them. The first step is the formation of a little scale of dentine 

 upon the apex of the pulp ; in the molar teeth there are at first 

 several of these scales, corresponding with the several elevations 

 of the pulp, but they soon coalesce. Immediately after the 

 appearance of this dentinal scale, a thin layer of enamel is de- 

 posited from the so-called enamel organ upon the roof of the sac, 

 and which coalescing with the dentine, forms the first rudiment 

 of the crown of the tooth. The scale of dentine extends over the 

 pulp and becomes thicker, so that it soon rests like a cap upon the 

 pulp, and finally forms a sort of capsule for it, which, as ossifica- 

 tion proceeds and the pulp diminishes, closely and completely 

 embraces it; the deposition of enamel goes on simultaneously, so 

 that it soon proceeds from the entire surface of the enamel organ, 

 and becomes more and more considerable. In this manner, the 

 whole enamel is eventually deposited around the dentinal layer of 

 the crown, while the enamel organ and the pulp gradually 

 diminish, until the former is represented only by a delicate mem- 

 brane ; and the latter presents similar. relations to that of the per- 

 fect tooth. As yet there exists no trace of either fang or cement; 

 they are not formed till the crown is nearly complete, and the 

 tooth is about to emerge. About this time the pulp under- 

 goes a considerable longitudinal growth, while the enamel organ 

 becomes atrophied ; and upon the newly formed portion only 

 dentine, that of the fang, is developed. The tooth, thus forced 

 upwards, begins to press against the upper wall of its sac, and 

 the firm gum which is closely united with it ; in which an in- 

 dependent process of absorption also takes place, and the tooth 

 finally makes its appearance. The gum now contracts around 

 it, and the rest of the dental sac becomes closely applied to the 

 fang, and constitutes the alveolar periosteum. 



The milk-tooth attains completeness : 1. by the addition of 

 the remainder of the fang, and the consequent elevation of the 

 crown to its normal length ; and 2. by a deposition which 

 takes place from the sac, now united with the alveolar periosteum, 

 which commenced even before eruption, and by which the 

 cement is applied around the fang, while at the same time 

 the tooth is thickened by internal deposition, the pulp 

 diminishing to a corresponding extent. In teeth with several 

 fangs, the pulp, which is at first simple, divides as it elongates, 



