508 



THE TEETH. 



stance, or matrix, is transparent and apparently homogeneous, while 

 the tubes, being (in a dried specimen) filled with air, are dark : but when 

 seen with reflected light on a dark ground the latter appear white ; in 

 these respects they resemble lacunas and canaliculi of bone. 



The dcnfiaal tubules open at their inner ends into the pulp-cavity, 

 which presents very numerous minute orifices over the whole surface. 

 Thence they pass in a radiated manner through every part of the ivory 

 towards its periphery. In the upper part of the crown they have a 

 vertical direction ; but towards the sides, and in the neck and root, 

 they become gradually oblique, then horizontal, and are finally even 

 inclined downwards towards the point of the fang. The tubules 

 describe in their course two or three gentle curves {primary curvatures, 

 fig. 201), and each is besides twisted throughout its whole length 



into numerous fine spiral turns, which 

 follow more closely one upon another ; 

 these are the secondary curvatures 

 (fig. 208). In form a tubule may 

 accordingly be likened to the thread 

 of a corkscrew, stretched so that the 

 turns are drawn far apart, and their 

 breadth proportionally diminished 

 (Welcker). 



The tubes are only shghtly di- 

 vergent as they pass towards the sur- 

 face ; and, as they divide several 

 times dichotomously, and at first with- 

 out being much diminished in size, 

 they continue to occupy the sub- 

 stance of the dentine at almost equal 

 distances, and their nearly parallel 

 primary curvatures produce, by the 

 manner in which they reflect the 

 light, an appearance of concentric 

 undulations in the dentine, which 

 may be well seen with a low magni- 

 fying power {Schrcyer's lines). The 

 average diameter of the tubules at 

 their inner and larger ends is 45Voth 

 of an inch, and the distance between 

 adjacent tubules is commonly about 

 two or three times their width. 

 From their sides numerous immeasur- 

 ably fine branches are given off, 

 which penetrate the hard intertubu- 

 lar substance, where they either anas- 

 tomose or terminate blindl}^ These 

 lateral ramuscules are said to be more 

 abundant in the fang. Near the peri- 

 phery of the ivory they are very 

 numerous, and, together with the 

 main tubules themselves, which there 

 by rapid division and subdivision, 

 also become very fine, terminate imperceptibly by free ends, or by join- 



Fig. 208. —Section of Fang, Faral- 

 lel to the dentinal tubules 

 (Human Canine). Magnified 300 

 DIAMETERS. (Waldeyer). 



1, cement, with large bone-lacunse 

 and indications of lamellise ; 2, granular 

 layer of Purkinje (interglobular spaces) ; 

 3, dentinal tnhules. 



