492 SPECIAL HISTOLOGY. 



be isolated, with special walls wliich are not those of the original cells, 

 and the same is true of the Haversian canals, whence it would be con- 

 ceivable that the walls of the dentinal canals also, although originally 

 and genetically not special structures, might eventually become so. 

 Since, again, the processes of the dentinal cells may be nothing else 

 than the still soft part of the cells in which ossification is commencing, 

 this first hypothesis may be regarded as having a certain claim to con- 

 sideration, the more so as the osseous lacunar in the teeth frequently as- 

 sume forms resembling those of the dentinal canals, often communicate 

 with them, and, at least in animals, are interposed among them. 



To sum up, it may be said, that in any case, the matrix of the dentine 

 proceeds from the cylindrical cells investing the pulp of the tooth, which 

 undergo a greater or less elongation, coalesce and ossify. The dentinal 

 canals either arise from the nuclei of these cells, or are, and this at 

 present appears to me to be more probable, the remains of the cavities 

 of the cells, whose boundaries have undergone a greater consolidation, 

 and therefore correspond with osseous lacunce. The divisions of the 

 canals are explained, if we conceive, either that the dentinal cells divide 

 longitudinally from time to time, as I believe I have actually observed, 

 or that a cell coalesces Avith two of its predecessors. As to the more 

 delicate ramifications, we can only suppose that they are formed by a 

 secondary process of resorption in already formed dentine, like that 

 which must be assumed to occur in the osseous lacuna', to account for 

 the anastomoses of their canalicuU, and their communication with 

 Haversian canals ; at least, I see no possibility, whatever view we take, 

 of explaining their formation in any other way, without coming into 

 opposition with well-ascertained facts. No such process as the thicken- 

 ing and ossification of dentinal cells accompanied by the formation of 

 pore-canals can be observed, so that the fine lateral branches appear to 

 be entirely of secondary origin. 



In the course of the ossification of the dentine, at least in man, we 

 find that the deposition of calcareous salts in the recently-formed, 

 structurally characterized, though only slightly hardened dentine, takes 

 place in such a manner that the whole appears to consist of isolated 

 globules. These globules, which are visible not only at later periods, 

 but in the earliest cap of dentine, and are best seen at the edge of the 

 root of a large tooth viewed externally, eventually disappear if develop- 

 ment proceed normally, calcareous matter being deposited between 

 them, so that the dentine becomes quite homogeneous and clear; in the 

 opposite case, they persist in greater or less number, and the spaces 

 between them, which are nothing but the interglobular spaces above 

 described, contain unossified dentine. 



According to my observations, the development of the cement takes 

 place from that portion of the dental sac which lies between the pulp 



