ELEPHANT. 645 



with wider intervals and a more wavy and irregular course than the 

 normal tubes of the ivory. 



The portion of the cement-forming capsule surrounding the base 

 of the tusk, and the part of the pulp, which were perforated by the 

 ball in its passage, are soon replaced by the active reparative 

 power of these highly vascular bodies. The hole formed by the 

 ball in the base of the tusk is then more or less completely filled 

 up by a thick coat of cement from without and of osteo-dentine 

 from within. Traces of such a cicatrix closing the entrance have 

 been more than once noticed : and Blumenbach deduced, there- 

 from, a property in the Elephant's tusk to pour out bony matter 

 in order to heal such wounds. The reparation is, however, effected 

 by the calcification of the reproduced parts of the capsule and 

 pulp. 



By the continued progress of growth, the ball so inclosed is 

 carried forwards, in the course indicated by the arrow in PI. 146, fig. 1, 

 to the middle of the sohdified exserted part of the tusk, as in the 

 example in Blumenbach^s collection which he considered so curious. 

 Should the ball have penetrated the base of the tusk of a youno- 

 Elephant it may be carried forwards by the uninterrupted growth 

 of the tusk until that base has become the apex, and be finallv 

 exposed and discharged by the continual abrasion to which the 

 apex of the tusk is subjected. Yet none of these phenomena 

 prove the absolute non-vascularity of the tusk, but only the low 

 degree of its vascularity. Blood circulates, slowly no doubt, through 

 the minute vascular canals which are continued through the centre 

 of the ivory to the very apex of the tusk : and it is from this 

 source that the fine tubular structure of the ivory obtains the es- 

 sential plasmatic colourless fluid by which its low vitality is 

 maintained. 



In order to obtain a complete and connected view of the micro- 

 scopic structure of the molar teeth of the Elephant, I made vertical 

 and transverse sections of the first molar, which, from its small size 

 permits the entire course of the dentinal tubes to be traced. 



The tooth examined was from the lower jaw, and was com- 

 pletely formed ; the two fangs being of their full length. The pulp- 



