ELEPHANT. 647 



diameter is Jo^th of an inch : they are much less wavy than in the 

 human teeth. The enamel fibres cross the plane of the layer 

 on a less transverse direction than that of the ends of the tubes 

 of the dentine directed towards the enamel : the outer surface to 

 which the cement is attached, shows more pits and irregularities 

 than that attached to the dentine. 



A well-defined layer of cement covers the bottom of the crown 

 at the interspaces of the two fangs, and extends over these to their 

 extremity. The sub-circular or full-elliptic radiated cells are closely 

 arranged, with their long axes parallel with the surface of the 

 cement ; numerous minute cemental tubuli run parallel to that sur- 

 face, and communicate with the radiated tubes of the cells and 

 with the terminal ramifications of the dentinal tubuli. The larger 

 vascular canals are present only in the thicker deposit of cement 

 at the bottom of the interspaces of the coronal plates. 



Dr. Falconer having kindly permitted me to take a longitudinal 

 section from a rare specimen of the first upper molar of the Elephas 

 planifrons, one of the extinct species whose remains he has discovered 

 in the Himalayan tertiary beds, I am able to give the following 

 comparison of the microscopic structure of this tooth, and that of 

 the nearly allied existing Indian Elephant. 



The dentinal tubuli are as minute and as closely aggregated ; they 

 have the same general direction and primary curve ; in parts of the 

 dentine, as at the summits of the conical sections of the lamellar 

 divisions of the crown, their secondary undulations are as minute 

 and irregular ; but the number of the strong undulations along the 

 contour lines at the middle of the dentinal cone is greater. The 

 strongest contour lines are accompanied by the strong undulations, 

 but there are many other lines which appear to be formed by a 

 slight opacity of the basal substance as in the Rhinoceros. 



The stratum of opake cellules near the peripheral ends of the 

 tubes is thicker ; the terminal bifurcations and occasional anastomotic 

 loops are the same as in the Indian Elephant. The enamel is thicker, 

 and the component fibres are more flexuous in the El. planifrons, 

 but in their size and other characters they agree with those of the 

 recent species, The cells of the cement which covers the crown and 



