38 ON THE ORIGIN AND DEVELOPMENT OF THE 



space. The pulp continues to lengthen till its base is no 

 larger than the fasciculus of vessels and nerve which enters it. 

 The orifice of the cavity of the tooth also diminishes to the 

 same size, and through it the surface of the pulp becomes 

 continuous with the adherent portion of the sac and con- 

 sequently with the mucous membrane of the mouth. The 

 adherent portion of the sac has now attained its maximum, 

 and the free or open portion its minimum size, having been 

 reduced to that narrow portion of the gum which forms a 

 vascular border and groove round the neck of the perfected 

 tooth.* 



During the period that the milk-teeth have been advanc- 

 ing along with their sockets to their perfect state and ultimate 

 position in the jaw, the permanent sacs have been receding in 

 an opposite direction, and have, as well as their bony crypts, 

 been enlarging, the edges of the latter, insinuating themselves 

 so far between the former and the milk-sacs, that at last they 

 are only connected by their proximal extremities, and ulti- 

 mately, when the lower edges of the crypts sink so far as to 

 have become the posterior lips of the alveoli of the milk-teeth, 

 the notches of communication between the latter and the 

 permanent alveoli are forced, under the form of foramina, 

 into a position on the anterior surface of the palate, one 

 behind each milk-alveolus. The sacs of the bicuspids having 

 assumed a position directly above the milk-molars, the hole 



* Tliis vascular border may be seen in healthy gums which have not been 

 disturbed bj' the deposition of tartar, and is beautifully displayed in two wet 

 injected preparations in the Bell collection, Museum of the Royal College of 

 Surgeons, Edinburgh (Bell, C. iii. Nos. 25 and 56). 



It is interesting to observe that one of the first physiological effects of mer- 

 cury — viz. excitation of the gastro-intestinal compound glands and simple 

 mucous follicles — is also displayed in a similar manner in the borders which 

 suiTound the necks of the teeth, which are the remains of the free portions of 

 the tooth-sacs, while it at the same time acts upon the adherent portions and 

 their submucoiis tissue, raising the teeth from theii" sockets, and affecting the 

 jaw from contiguity. 



