284 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



Fig. 



sionally divide dichotomously; and they frequently give off minute branches, 

 which again send off smaller ones. These branchings are more frequent, the 

 nearer the tubes approach the exterior of the dentine; and indeed it is only in 

 the immediate neighborhood of the enamel, that the dentinal tubes of the crown 

 of the human tooth usually begin to ramify, although those of the neck and 

 fang give off branches about the middle of their course. The terminal branches, 

 on their arrival at the line of junction between the dentine and enamel, some- 

 times recurve and anastomose with contiguous tubes, sometimes pass across the 

 line of junction and extend themselves for a short distance into the enamel 

 (as first noticed by Mr. Tomes), 1 and sometimes end in a fine point or in a 

 rounded dilatation. In the fang of the tooth, there is a much more frequent 

 anastomosis among the tubuli; and of their terminal branches, some lose them- 

 selves in their intertubular tissue, others dilate into radiating cells not unlike 

 those of the cementum, others anastomose and form loops with the branches of 

 adjacent tubes, whilst others pass into the interspaces that exist among the large 



granules that form the outer surface 

 of the dentine of the fang (Fig. 74, b 

 6), and some of these may even ex- 

 tend themselves into the cementum 

 and communicate with its radiating 

 cells. When the dentinal tubuli are 

 examined in transverse section (Fig. 

 75), the aperture of each is seen to be 

 surrounded by an annulus, which se- 

 parates its parietes from the intertu- 

 bular tissue ; and it can be further seen, 

 better in transverse than in longitu- 

 dinal sections, that the distances of 

 the tubuli from each other vary great- 

 ly; the tubuli being closest, and the intertubular tissue consequently the small- 

 est in amount, in the crown of the tooth (A) ; whilst in the dentine of the fang 

 the intertubular tissue forms the larger element (B). The internal diameter of 

 the tubuli in their largest part averages about 1-10, 000th of an inch; but when their 

 parietes are included, it measures about 3-10,OOOth; their smallest branches are 

 immeasurably fine. The intertubular tissue of dentine, as of bone, is affirmed 

 by Mr. Tomes to be granular throughout; the granules being nearly spherical, 



and measuring from 1 to 3-10,OOOths. Near the 

 surface of the dentine in the fang, and occasionally 

 in other parts of the tooth, it presents the appear- 

 ance of an aggregation of nodular concretions, with 

 irregular interspaces between them (Fig. 74, b b) ; 

 each of these, when divided transversely and 

 highly magnified, is seen to be traversed by se- 

 veral dentinal tubes (Fig. 76). In other parts of 

 the tooth, it not unfrequently happens that the 

 dentinal substance is traversed by lines which 

 divide.it into more or less regular polygonal areae; 

 and this appearance, which is normal in the teeth 

 of many of the lower animals, is considered by 

 Prof. Owen as indicative of the persistence of the 

 boundaries of the original cells of the pulp. A more satisfactory explanation 



1 See his "Lectures on Dental Physiology and Surgery," p. 35. Mr. Tomes has since 

 shown that the passage of the dentinal tubes into the Enamel, in large numbers, and for 

 a considerable distance, is a distinctive character of the teeth of Marsupialia. "Philos- 

 Transact,," 1849. 



Transverse sections of Dentine ; |, from the crown; 

 B, from the fang ; showing the orifices of the tubes, and 

 the thickness of their walls. 



Fig. 76. 



Portion of the nodular layer of the 

 Dentine oftticfang, more highly mag- 

 nified. 



