SECT. 141.] DEVELOPMENT OF TISSUES OF THE TOOTH. 307 



1. Tlie dentinal canals are direct processes of the whole dentinal cells, which 

 processes may send out subordinate branches, and anastomose by means of 

 them. To all appearance, a single cell seems, in many cases, to be sufficient 

 to form an entire dentinal canal, or at least a very large part of one. 



2. The matrix of the dentine is not formed of the dentine-cells, but is a 

 secretion oj these cells and oj the tooth-pulp : in other words, an intercellular 

 substance. 



Taking all these facts together, it results, that the canals of the dentine 

 arise by the direct metamorphosis of a histological element of the pulp, viz., 

 the dentinal cells, whilst the matrix of the dentine is to be regarded as a 

 secretion from these cells and the vessels of the pulp. My opinion thus 

 holds a middle place between the old excretion-theory, according to which 

 the whole dentine is an excretion of the pulp, and the theory of metamor- 

 phosis, according to which it is constructed, entirely and alone, out of certain 

 histological elements of the pulp. On the other hand, I cannot accede to 

 the deposition-theory of Huxley, according to which the dentine is deposited 

 in the pulp without any of the histological elements taking part in its 

 formation ; but I agree with him in this, that the formation of dentine takes 

 place beneath the membrana praformativa. Moreover, I may further observe 

 that in animals, and perhaps in man, an ossification of the inner part of 

 the pulp appears to occur as a pathological condition ; for we meet with 

 dentine containing vessels (vaso-dentine, Owen), according to Tomes, even in 

 man ; and in the teeth of certain animals, the pulp is entirely absent. In 

 such cases, the pulp simply ossifies, probably like connective tissue, which 

 also agrees very well with the fact, that the vaso-dentine much more resembles 

 ordinary bone than dentine. 



During the ossification of the dentine a deposition of calcareous salts takes 

 place, at least in man, in the newly-arisen, morphologically characterised, but 

 still little hardened dentine, frequently in such a manner that the whole 

 appears to consist of isolated globules. These globules, which are seen both 

 in the primitive scales of dentine and in later stages, — especially at the border 

 of a fang of a larger tooth, when viewed from the outer side, — subsequently 

 disappear when the formation of dentine goes on normally, calcareous earth 

 being deposited between them, so that the dentine becomes quite homo- 

 geneous and more translucent ; in the opposite case, they remain persistent 

 in larger or smaller numbers, and the spaces between them, which are merely 

 the above-mentioned intei'globular spaces, contain incompletely ossified 

 dentine. 



The formation oj the cement proceeds, according to my observations, from 

 that part of the tooth-sac wdiich is situated between the pulp and the enamel- 

 organ, and commences even before the eruption of the tooth, as soon, indeed, 

 as the fang begins to be formed. At this period, the tooth-sac becomes elon- 

 gated at its lower part, is closely applied to the developing fang, and, from its 

 rich network of vessels, furnishes — as the periosteum does during the growth 

 in thickness of the bones — a soft blastema, in which nucleated cells become 

 developed, and which then immediately ossifies. Accordingly, the cement is 

 not formed by the ossification of the tooth-sac itself. I observed the first 

 traces of it in newly-born infants, in the form of isolated scales of an elon- 

 gated or roundish shape, which firmly adhered to the dentine of the still very 

 short fangs, and looked exactly like the developing osseous substance in 



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