318 ORYCTEROPUS. 



and external sides, giving their transverse section a bilobed or 

 hour-glass figure : the seventh molar is smaller, and has the same 

 simple figure as the fourth. 



The first molar in the lower jaw is similar in size and shape to 

 the second of the upper jaw to which it is opposed ; in one of the spe- 

 cimens examined by me, it was shed, and every trace of its alveolus 

 effaced, leaving only five molar teeth in the lower jaw. In this bone, 

 which measured eight inches in length, the molar series occupied 

 an extent of two inches, commencing about three inches and a 

 half from the anterior extremity of the ramus : the dentigerous 

 part of the bone is slightly expanded, both laterally and inferiorly. 

 The antepenultimate and penultimate molars of the lower jaw are 

 indented, like those above, by a longitudinal groove upon both their 

 outer and their inner sides, which grooves sink rather deeper into 

 the substance of the tooth, as they approach the base. 



The proportions of these teeth, the depth of their sockets, and 

 their structure, as viewed in longitudinal section with the naked eye, 

 are shown in Plate 76, Fig. 10. The teeth are continued sohd, 

 and of the same dimensions, to the bottom of the socket, and 

 terminate by a truncated and undivided base. M. F. Cuvier and 

 other Comparative Anatomists have noted the distinction which 

 the teeth of the Orycteropus present, as compared with those of all 

 other animals, in the absence at every period of their growth of a 

 pulp-cavity at the base. But this difference is more apparent than 

 real ; it could only be predicated of the teeth in question, if each 

 was what it seems, a single tooth, and not as it really is an aggregate 

 of teeth. When viewed in the latter light, it will be found that each 

 component denticle has its base excavated by a conical pulp-cavity, as 

 in other animals, and which is persistent, as in the rest of the 

 order Bruta. The wide inferior apertures of these pulp-cavities 

 constitute the pores observable on the base of the compound tooth 

 of the Orycterope, and give to that part a close resemblance to the 

 section of a cane (1) : the canals to which these pores lead, are 

 the centres of radiation of the calcigerous tubes of the denticle, (2) 



(1) PL 76, fig. 11. 



(2) Report of the British Association, vol. vii. 1838, p. 145. 



