4 CHARLES S. TOMES. 



the pulp, and by their interlacing form the central bony core 

 of the tooth, which, when completed, cannot be said to have 

 any pnlp cavity. The tooth is attached to the subjacent bone 

 by a continuation of these calcifying rods down to the bone, 

 with which they coalesce, the shell of hard dentine thinning 

 down to nothing at the base of the tooth. The core of the 

 tooth and the subjacent bone are structures so similar that it 

 is absolutely impossible to find a line of demarcation between 

 the two in a completed tooth. 



The principal characters of the hinged teeth may be un- 

 derstood by an inspection of figs. 3 and 4. It will be seen 

 that the teeth are not solid, like the anchylosed tooth repre- 

 sented in fig. 2, but that there is a sort of pulp-chamber (b), 

 not AvhoUy filled up by calcified tissue, and that the teeth are, 

 as viewed by a low power (figs. 4 and 5), or in dried speci- 

 mens, connected with the subjacent bone only by means of a 

 hinge of fibrous tissue (e, fig. 4), the base of the tooth being 

 received upon a little pedestal of bone (/). The central 

 cavity is not, however, wholly empty, nor is it solely occu- 

 pied by soft pulp tissue ; from the interior of the shell there 

 run down rods of calcified tissue (h), which are roughly 

 parallel with the long axis of the tooth, and which become 

 slender and more transparent as they go down. 



In a favorable section the thin parallel strings into which 

 they dwindle may be seen to pass right down to the bone, 

 and as they approach the bone they become again thicker, 

 and blend insensibly with it (sec (j, fig. 5). These filaments 

 were at first a source of great bewilderment to me ; running 

 from the interior of its dentine cap sttaight down to the bone, 

 they would, if inelastic, tie the tooth down (see fig. 5), so 

 that unless they were broken the hinge would be a useless 

 superfluity, and their absolute straightness, apparent rigidity, 

 and high refractive index, made them look exceedingly 

 brittle ; they were often broken, but never curved nor bent 

 in the sections. However, reiterated examinations have de- 

 monstrated that they are not calcified in their whole length ; 

 they are calcified where they start from tlie dentine cap, and 

 apparently again where they blend with the bone, but the in- 

 termediate ])ortion reinaius soft ; 'and the resumption of the 

 upright position by the tooth, after being bent down, is wholly 

 du(! to the elasticity of tliese fibrils ; if they are carefully divi- 

 ded, the hinge being left wholly uninjured, the tooth remains 

 in any position in which it is left. They are thus capable of 

 great extension, and are very perfectly elastic, a depressed 

 tooth springing back to its upright position with an audible 

 snap. 



