Mr. Owen on the Zeuglodon cetoides. 71 



of the tooth, hecomes contracted as the fangs descend, and is almost obhterated 

 near their extremities, proving that the pulp of the teeth once calcified is not 

 renewed, so that their growth is limited. 



In a fractured anterior portion of the hindmost tooth, the pulp-cavity is seen 

 to widen as the tooth descends in the jaw ; it is not, however, surrounded, as in 

 the section above-described, by concentric striae, but enlarges towards that side 

 next the posterior portion of the tooth, as if it were continuous with the enlarged 

 pulp-cavity of that portion ; from this appearance it is evident that the growth of 

 this tooth was less advanced than the preceding, as might be expected from its posi- 

 tion in the jaw. The sockets in the anterior fragment of the upper jaw were filled 

 with the hard calcareous matrix, and their condition and extent were but obscurely 

 seen : the first is described as being the socket of a double molar, i. e. of a molar 

 with two distinct fangs, and the two corresponding cavities are so represented in 

 Dr. Harlan's work*. To remove all doubt upon this point, I have caused to be 

 made a transverse horizontal section of the alveolar margin, which shows clearly 

 that the sockets of both the absent teeth are single, and that they had single 

 fangs. In the anterior one there is an indication of the transverse median con- 

 traction of the tooth, which shows that this tooth resembled in form, to a certain 

 degree, the posterior tooth. The longest diameter of this socket is two inches, 

 four lines, the shortest one inch. The other socket is of a more simple form, viz. 

 elliptical, measuring one inch, five lines, by eleven lines; it appears to have origin- 

 ally lodged a tooth further displaced from the jaw. The interspace between these 

 teeth is one inch, five lines ; the interspace between the second tooth and the one 

 behind it, one inch, ten lines. 



Of the fragment of the lower jaw of the Zeuglodon there is a plaster-cast in the 

 Society's Museum. It contains four teeth, of which the two posterior are neatly 

 contiguous ; the next is separated from them by an interval of an inch and a hali', 

 and the most anterior is placed at a distance of two inches from the preceding. 

 The anterior tooth is here of smaller size and apparently of more simple form than 

 those behind, and it is described by Dr. Harlan as a canine. This interesting frag- 

 ment is preserved in the Museum of the Phiiadelphian Academy ; it confirms the 

 evidence afforded by the fragments of the upper jaw, viz. that the teeth in the 

 Basilosaur were of two kinds, the anterior being smaller, more simple in form and 

 more remote from each other, than those behind. 



Now the animals which have teeth lodged in distinct alveoli, and with which 

 therefore we have to compare the Zeuglodon, are certain fishes, as the Sphyrcena 

 and its congeners ; certain reptiles, as the plesiosauroid and crocodilian Sauria, 



* Loc. cit. (Fig. 1. B.C. PI. XXVI.). 



