570 UNGULATES. 



to the surrounding parts, inflammation of the pulp and capsule 

 had ensued, ending in an altered mode of action in the calcifying 

 processes, which produced the substance, called from its nearer 

 resemblance to bone ' osteo-dentine.' In this substance is seen the 

 transition of the normal dentinal tubes into the radiating tubes of 

 the calcigerous cell ; and a well-marked stage in the transformation 

 of dentine into bone. In ordinary teeth the change in the mode 

 of conversion of the last part of the pulp is sometimes so gradual as 

 to render the confluence of the dentine with the osteo-dentine com- 

 plete ; and the present instance demonstrates the same confluence of 

 the osteo-dentine with the ivory of the upper part of the tusk 

 formed before the fracture, and with that at the base formed after 

 the fracture, when the ordinary processes in the development of 

 the tusk had been resumed. In the complete resumption of these 

 processes, after the entire conversion of the matrix at the fractured 

 part of the tusk into the mass of osteo-dentine which constitutes 

 the uniting medium, we have a striking example of the truth of 

 the conversion-theory of dental development. It will scarcely be 

 contended that the calcified substance which manifests, besides the 

 complex tortuous tubuli, numerous concentric series of radiated 

 purkingian cells, and the larger vascular or medullary canals, called 

 ' Haversian,' in osteology, is the product of a disordered secretion 

 of a pulp inflamed by injury; we see, on the contrary, evidence of 

 the conversion of such altered pulp by a series of centripetal 

 processes of calcification, resulting in the aggregate of subspherical 

 nodules of the osteo-dentine. Now, if the pulp of a continually 

 growing tusk were a persistent secreting organ, an accident 

 occasioning such destruction of it as is manifested by the microscopic 

 structure of the mass uniting the fractured parts of the Hippopo- 

 tamus's tooth under consideration, must have put an end to the 

 secreting actions of such matrix, and to the future formation of the 

 tusk. But here, on the contrary, it is shown that the inflammatory 

 effects of the injury terminated in the abnormal conversion of the 

 affected pulp into a bone-like substance, and yet that the subsequent 

 development of the tusk was effected by the reproduction of a 

 vascular basis or pulp, undergoing the ordinary processes of calcifica- 

 tion to which the formation of the dentine, enamel and cement is due. 



