ORYCTEROPUS. 319 



and not the orifices of simple canals resembling, as it was supposed, 

 those of baleen or Rhinoceros-horn, (1) 



The compound tooth of the Orycterope consists of a congeries 

 of very long and slender prismatic denticles commonly six-sided, more 

 rarely five or four-sided, cemented together laterally, slightly de- 

 creasing in diameter, and occasionally bifurcating as they approach 

 the grinding surface of the tooth. The medullary or pulp-canal 

 of each denticle is widest at its base (PI. 11 ^ a, a,) diminishes at 

 first rapidly, then very gradually, and divides where the denticle 

 divides, to continue along the centre of each division. The walls 

 of the denticle consist of hard un vascular dentine, into which the 

 minute calcigerous tubes are sent from every part of the circum- 

 ference of the medullary canal (PI. 78). The calcigerous tubes 

 are ^th of a line in diameter at their origin ; but rapidly diminish as 

 they proceed, dichotomously sub-dividing, towards the interspace which 

 separates them from the contiguous denticles : their general course 

 is transverse to the axis of the denticle, and they give off" numerous 

 branches, which form near the boundary space a moss-like reticulation 

 of extremely minute tubes. Nearly the whole extent of the medullary 

 canal is occupied by a vascular pulp, and the base of each denticle 

 is surrounded by a delicate vascular capsule, which becomes ossified 

 about a Hne above the base, and forms the cementing substance 

 of the congeries of denticles. The vascular pulp, likewise, becomes 

 ossified near the grinding surface of the tooth, and consequently a 

 transverse section taken from this part, presents the centres of the 

 radiation of the calcigerous tubes filled up with bone. 



From the preceding account of the minute structure of the 

 compound tooth of the Orycterope, it will be seen to resemble the 

 teeth of the Myliobates and Chimseroids, among fishes, rather than 

 any true teeth in the MammaHan class, in which it offers a tran- 

 sitional step from the horny substitutes of teeth, above described 

 to the true teeth. 



The teeth of the Orycteropus, when rightly understood, offer, 

 however, no anomaly or exceptional condition in their mode of 



(1) Cuvier, Lemons d'Anat. Comp. ed. 1836, t. iii. p. 205. Heusinger Histologic, 1823, 

 p. 198. 



