648 UNGULATES. 



fills part of the interspaces of the coronal plates are sub-circular, 

 with often a slightly angular outline ; they are densely aggregated. 

 There are no vascular canals in the thinner layer of cement which 

 covers the fang, but these are always present in the thicker cement of 

 the crown. 



In portions of larger molars of the Indian Elephant which I have 

 examined, the dentinal tubes have the same minuteness and close 

 arrangement, and the same general primary curve, as in the small 

 first molar ; but the extent to which they manifest the strong undu- 

 lations characteristic of ivory is greater(l). In old molars the pulp- 

 cavity becomes in part obliterated by the modified ivory called osteo- 

 dentine, and the tubes in the dentine of the roots describe nume- 

 rous considerable undulations. The enamel does not extend upon 

 the roots but terminates, as in other teeth, at the base of the crown ; 

 the cement is continued in a thin layer to the end of the roots 

 (PI. 150, fig. 2, c c), and there becomes continuous with the osteo- 

 dentine which fills the central part of the pulp-cavity. The disposi- 

 tion of the calcigerous tubes in a longitudinal section of one of the 

 fangs, with the central osteo-dentine, and the peripheral cement is 

 shown in PL 150. The dentinal tubes come off from the clear part 

 of the osteo-dentine by fasciculi, in certain parts of the pulp-tract ; 

 they are minutely and irregularly undulated throughout the course of 

 the stronger undulations which here assume the character of primary 

 curvatures. The terminations of the tubes at the semi-opake peri- 

 pheral tract, along which the minute opake cellules are dispersed, 

 seem to dilate slightly, and to be less sharply defined (ib. fig. 1, d^\) 

 Many of the terminal branches of these tubes pass into the 

 cement, and anastomose with the fine tubes of that tissue ; the 

 cemental tubes are largest at its peripheral part (ib. c''). 



231. Development. — The matrix of the tusk consists of a large 

 conical pulp, which is renewed quicker than it is calcified, and thus 

 is not only preserved, but grows, up to a certain period of the 

 animal's life : it is lodged in the cavity at the base of the tusk ; 

 this base is surrounded by the remains of the capsule, a soft 



(1) These undulations produce on the fractured surfaces of the dentine of the molars in 

 which they occur, the engine-turned character of true ivory. 



