CHAP. XXIII.] DEVELOPMENT OE THE TEETH. 177 



which remains in the interior of the tooth after its development has 

 been completed. The chief vascularity of the pulp is uniformly 

 found near the ossifying surface, whence it is evident that the 

 earthy materials are supplied from that source. In the teeth of 

 some animals, in which the dentine is penetrated by many subor- 

 dinate offsets from the central cavity, containing blood-vessels, 

 these passages are left in the progress of development, just as has 

 been above described. 



It has been already said, that the reflexion of the original mucous 

 membrane of the follicle on to the papilla takes place at a line 

 corresponding nearly to the neck of the future tooth, and that the 

 original papilla answers to the crown or body of the tooth, and not 

 to the root. This latter is a subsequent formation, and is laid down 

 gradually after a certain amount of ossification has already taken 

 place in the crown, and after the enamel has been calcified. It is 

 formed and ossified by a process precisely similar to that of the 

 dentine of the crown, only a more protracted one, and during 

 which the tooth is raised out of its sac, and bursts the contain- 

 ing gum. The lengthening of the fang preceding its ossifica- 

 tion resembles closely that occurring at the junction of the shaft 

 with the epiphyses of the long bones during their development 

 ( vol. i. p. 121). 



The calcification of the enamel commences on the surface of the 

 dentine, in contact with that primary osseous sheet formed from the 

 basement membrane of the dentinal pulp. On this primary layer 

 are minute shallow cups, closely aggregated, answering to the ends 

 of the enamel columns, and receiving them in a firmly cemented 

 union, as the consolidation of the elementary cells proceeds. The 

 enamel columns at a very early stage seem to consist only of a 

 single series of nucleated particles, intervening between the dentine 

 and the enamel-pulp; but subsequently others are added on the 

 surface towards the enamel-pulp. Those of the new row arrange 

 themselves endwise on the others, which they resemble in all re- 

 spects, so that the enamel attains its proper thickness rather by the 

 superposition of particle on particle, successively deposited, and by 

 the subsequent calcification of each in its turn, than by the deve- 

 lopment of its parts by an interstitial increase ; and thus it appears 

 to differ from the dentinal pulp, and to resemble the epithelium, to 

 which it is allied. 



It is from that surface of the enamel-pulp which looks towards 

 the tooth, that this successive development of new enamel columns 

 proceeds ; as they form, this tissue wastes ; but it is not probable 



VOL. II. N 



