930 



TEETH. 



not been formed upon the surface and in the 

 interspaces of the pulp-plates. 



Coincident, however, with the formation 

 of the dentine, is the deposition of the hard- 

 ening salts of the enamel in the extremely 

 slender prismatic cells, which are for the most 

 part vertical to the plane of the inner surface 

 of the folds of the capsule to which they are 

 attached ; these cells or moulds give a sub- 

 transparent bluish tint to the enamel pulp. 

 The true inner part of the capsule forms 

 those thick transverse folds or partitions which 

 support the enamel organ, and with it fill the 

 interspaces of the dentinal pulps. With re- 

 gard to the formation of the cement, Cuvier, 

 after citing the opinion of Tenon that it 

 was the result of ossification of the internal 

 layer of the capsule, and that of Blake that 

 it was a deposition from the opposite surface 

 of the capsule to that which had deposited 

 the enamel, states his own conviction to be 

 that the cement is produced by the same 

 layer and by the same surface as that which 

 has produced the enamel. The proof alleged 

 is, that so long as any space remains between 

 the cement and the external capsule, that 

 space is found to contain a soft internal layer 

 of the capsule with a free surface next the 

 cement. The phenomena could not, in fact, 

 be otherwise explained according to the " ex- 

 cretion theory " of dental development. To 

 the obvious objection that the same part is 

 made, in this explanation, to secrete two 

 different products, Cuvier replies, that it un- 

 dergoes a change of tissue : " Whilst it yielded 

 enamel only it was thin and transparent ; to 

 give cement it becomes thick, spongy, and of 

 a reddish colour." * The external characters 

 of the enamel organ and cement-forming cap- 

 sule are correctly defined ; only, the one, in- 

 stead of being converted into the other, is in 

 fact changed into its supposed transudation : 

 the enamel fibres being formed, and properly 

 disposed in the direction in which their chief 

 strength is to lie, by the assimilative proper- 

 ties of the pre-arranged elongated prismatic 

 non-nucleated cells, which take from the sur- 

 rounding plasma the required salts and com- 

 pact them in their interior. 



Whilst this process is on foot, and before 

 the enamel fibres are firm in their position, 

 the capsule begins to undergo that change 

 which results in the formation of the thick 

 cement; the calcifying process commences 

 from several points, and proceeds centrifu- 

 gally, radiating therefrom, and differing from 

 the ossification of bone chieflv in the number 

 of these centres, which, though close to the 

 new-formed enamel, are in the substance of 

 the inner vascular surface of the capsular 

 folds. The cells arrange themselves in con- 

 centric layers around the vessels, and act 



* " Seulement elle change de tissue : tant qu'elle 

 ne donnait que de 1'email, elle Aait mince et tvai-s- 

 parente ; pour donner du cortical elle devient epaisse, 

 spongieuse, opaque et rougeatre." Annales dii 

 Museum, torn. viii. p. 99; Ossemens Fossiles, ed. 

 1834, 8vo. torn, i p. 514. Art. PACHYUKHMATA, 

 p. oOy. 



like those of the enamel pulp in receiving into 

 their interior the bone-salts in a clear and 

 compact state; during this process they be- 

 come confluent with each other, their piimi- 

 tive distinctness being indicated only by their 

 persistent granular nuclei, which now form 

 the radiated Purkinjian corpuscles. The in- 

 terspaces of the concentric series of confluent 

 cells become filled with the calcareous salts 

 in a rather more opaque state, and the con- 

 version of the capsule into cement goes on, 

 according to the processes more particularly 

 described in the Introduction to my " Odon- 

 tography," until a continuous stratum is formed 

 in close connection with the layer of enamel. 



The uncalcified part of the capsule, always 

 much softer than cartilage, is very readily 

 detached from the calcified part, and to the 

 naked eye the separated surface seems entire, 

 and might readily pass, as with Cuvier, for 

 a secreting surface. But the fine vascular 

 processes which have been torn from the 

 medullary canals of the calcified part are 

 conspicuous, and resemble villi, when the 

 detached surface is examined, even with a 

 moderate magnifying power, under water. 



Calcification extending from the numerous 

 centres, the different portions coalesce and 

 progressively add to the thickness of the ce- 

 ment until all the interspaces of the coronal 

 plates and the whole exterior of the crown is 

 covered with the bone-like substance. The 

 enamel-pulp ceases to be developed at the 

 base of the crown, but the capsule continues 

 to be formed pari passu with the partial 

 formation of the pulp, as this continues, pro- 

 gressively contracting, from the base of the 

 crown, to form by its calcification the roots. 

 The calcification of the capsule going on nt 

 the same time, a layer of cement is formed in 

 immediate connection with the dentine. The 

 circumscribed spaces at the bottom of the 

 socket to which the capsule and dentinal pulp 

 adhere, where they receive their vessels and 

 nerves, and which are the seat of the progres- 

 sive formation of these respective moulds of 

 the two dental tissues, become gradually con- 

 tracted, and subdivided by the further localis- 

 ation of the reproductive forces to particular 

 spots, whence the subdivision of the base into 

 roots. The surrounding bone undergoes cor- 

 responding modifications, growing and filling 

 up the interspaces left by the dividing and 

 contracting points of attachment of the re- 

 siduary matrix. All is subordinated to one 

 harmonious law of growth by vascular action 

 and cell-formation, and of molecular decre- 

 ment modifying form by absorption. Me- 

 chanical squeezing or drawing out have no 

 share in these changes of the pulp or capsule; 

 pressure at most exercises only a gentle 

 stimulus to the vital processes. Cuvier be- 

 lieved that there were places where the den- 

 tinal pulp and the capsule were separate from 

 each other. I have never found such except 

 where the enamel-pulp was interposed be- 

 tween them in the crown of the tooth, or 

 where both pulp and capsule adhered to the 

 periosteum of the socket, below the crown. 



