REPORT ON THE CETACEA. 11 



about the middle of the upper border of the fang. It was 7-lOths of an inch in its 

 basal diameter, and 4-lOths from apex to base. The fang was homologous with the 

 strap-shaped shaft in the adult tooth, but instead of being vertically elongated and strap- 

 shaped, its longer diameter of 2 inches was in the antero-posterior direction, whilst its 

 greatest vertical diameter to the base of the denticle was only 8-lOths of an inch. Along 

 its deeper border it possessed a cleft 2-lOths of an inch wide, which led into the pulp- 

 ca^'ity. On making a vertical section through the middle of the entire tooth, this cavity 

 was seen to be prolonged almost as far as the apex of the denticle (PI. II. figs. 15, 16). 



The free surface of the denticle was completely invested by a glistening white enamel. 

 A thin vertical section was then taken out of the middle of the tooth and polished for 

 microscopic examination. ^ The cap of enamel was then seen to be of almost uniform 

 thickness over the entire denticle, at the base of which it was somewhat overlapped by 

 an up-growth of cement from the fang. When highly magnified the surface of section 

 was seen to be marked by delicate bands, extending almost perpendicularly to the surface 

 of the denticle, which indicated the rods of which the enamel was composed. 



Subjacent to the enamel was a well-defined mass of dentine, which constituted the 

 chief substance of the denticle. It was traversed by undulating branched tubes,which 

 radiated outwards from the pulp-cavity, and were arranged with as much regularity as 

 one sees in the crown of a human tooth. Where the branched terminations of the dentine 

 tubes came into relation with the deep surface of the enamel, a layer of irregular, but 

 somewhat stellate, spaces occupied the dentine matrix. These spaces corresponded in 

 appearance with the so-called granular layer situated in human teeth more especially in 

 the fang, between the dentine and cement, and may be termed interglobular spaces (fig. 18). 



The dentine was prolonged downwards into the fang, and with a simple lens could be 

 traced almost as far as the edge of the cleft at its root, but it formed so thin a lamina in 

 the greater part of its extent, as to appear merely as a line in the unmagnified section. 

 When highly magnified, the dentine in the fang, immediately continuous with that in the 

 denticle, was seen to contain the tubes arranged in a regular manner, but as the dentine 

 was followed further into the fang, the tubes began to break up into irregular groups, 

 then to be sparsely scattered through the matrix, and at last to disappear, so that in the 

 lower part of the fang the dentine was represented by a translucent matrix, having 

 indefinitely-shaped granules irregularly scattered through it. 



The fang of the tooth was invested by a yeUowish-brown substance, Avhich was smooth 

 on its surface in proximity to the denticle, but in the region of the cleft was pitted with 

 shallow grooves and small foramina, so as to have a porous aspect. In the section this 

 substance was seen to vary in thickness, its maximum being 1-1 0th of an inch, and 

 becoming thinner both towards the denticle and the cleft. To the naked eye it was 



' This and succeeding sections were kindly mude for me in the Challenger Laboratory by my friend Jlr John 

 Murray. 



