

PULPS AND SACS OF THE HUMAN TEETH. 37 



the gum a process which is accomplished in the following 

 manner : The body of the tooth having been fully formed, 

 and coated with enamel, has also been acquiring a portion 

 of its fang by the triplex action formerly described ; in con- 

 sequence of which, a reaction takes place between the bottom 

 of the socket and the unfinished extremity of the fang. 

 This reaction causes the body of the tooth and the non- 

 adherent portion of the sac gradually to approach, and the 

 former finally to pass through the surface of the gum. Till 

 the time that the edge of the tooth passes through the gum, 

 the fundus of the sac, and consequently the base of the pulp 

 with the extremity of the fang, never change their common 

 relative position in the jaw. At the moment, however, that 

 the tooth passes through the gum (when the non-adherent 

 portion of the sac resumes its primitive follicular condition, 

 its inner membrane becoming continuous with the mucous 

 membrane of the mouth) the non-adherent portion of the sac 

 shortens more rapidly than the fang lengthens, in consequence 

 of which the adherent portion with the fang itself separates 

 from the fundus of the alveolus and the body of the tooth 

 advances through the gum.* A space is thus left between the 

 top of the alveolus and the fundus of the sac, occupied by 

 cellular tissue, and traversed by the vessels and nerves. The 

 alveolar cavity at the same time rapidly adapts itself to the 

 new condition of its contents, advancing its edges so as to 

 clasp the root, which has during these rapid changes been 

 steadily lengthening a process which now goes on with 

 greater rapidity, as it is conducted in a comparatively empty 



* The movement of the unfinished extremity of an incisive tooth from the 

 fundus of its alveolus will explain what I have commonly remarked, and what 

 must have been observed by medical practitioners, that from the time that the 

 edge of the tooth appears through the gum, it advances more rapidly than can 

 well be accounted for by the usual rate of lengthening of its fang. This ad- 

 vance is not invariably rapid, but may be observed in all the incisive teeth, if 

 careful daily examination be made during a normal dentition. 



