

STRUCTURE AND DEVELOPMENT OF DENTINE. 187 



occasionally divide into two branches, which continue to run at a little 

 distance from one another in the same direction ; and they also fre- 

 quently give off small lateral branches, which again send off smaller 

 ones. In some animals the tubuli may be traced at their extremities 

 into minute cells, or cavities, analogous to the lacunae of bone ; and the 

 lateral branchlets occasionally terminate in such cavities, which are 

 called the intertubular cells. The diameter of the tubuli at their largest 

 part, averages l-10,000th of an inch ; their smallest branches are immea- 

 surably fine. It is impossible that even the largest of them can receive 

 blood, as their diameter is far less than that of the blood-discs ; but it is 

 probable that, like the canaliculi of bone, they may absorb nutrient matter 

 from the vascular surface, with which their internal extremities are in 

 relation. 



312. In the Teeth of Man and of most Mammalia, we find the central 

 portion hollow ; and lined, in the living tooth, by a vascular membrane. 

 This cavity, with its vascular wall, is analogous to a large cancellus or 

 Haversian canal of Bone ; and, as we shall presently see, it is formed 

 in a similar manner. Upon the walls of the 



cavity, all the tubuli open ; and they radiate 

 from this towards the surface of the upper 

 part of the tooth, as shown in the accom- 

 panying figure. The central cavity is con- 

 tinued as a canal through each fang or root ; 

 and the dentinal tubes in like manner radiate 

 from this, towards the surface of the fang. In 

 the teeth of many of the lower animals, how- 

 ever, we find a network of canals extending 

 through the substance of the tooth, instead of 

 a single cavity ; and these canals are fre- 

 quently continuous with the Haversian canals 



Of the Subjacent bone, SO that the analogy Oblique section of Dentine of hu- 



between the two is complete. From^ each ^^^l^ 1 ^ 1 ^'- 

 canal the dentinal tubuli radiate, just in the 



manner of the canaliculi of bone ( 295) ; and thus we may regard a 

 tooth of this kind as repeating, in each of the parts surrounding one of 

 these canals, the structure of the human tooth. 



313. The process by which the cellular mass, or pulp, of the dental 

 papilla becomes converted into the Dentine of the perfect tooth, has not 

 been so clearly made out, as to be beyond all question. The following, 

 however, is the account given of it by Mr. Tomes,* who has very care- 

 fully examined it. The dentinal pulp is at first composed of a mass of 

 nucleated cells, held together by a meshwork of delicate fibres and 

 bands constituting an imperfect form of areolar tissue, the interspaces 

 between them being occupied by a homogeneous plasma. In the part 

 which is nearest to the coronal surface of the tooth when calcification^ 

 about to commence, the areolar tissue has usually disappeared, and its 

 place is occupied by a finely-granular gelatinous substance. The cell 

 are at first disposed without any regularity in the midst of this ; but 



* Lectures on Dental Physiology and Surgery. 



