251 
of Edinburgh, Session 1878-79 
by an opaque layer, consisting of a granulated matrix containing 
numerous branched and anastomosing vascular canals, like the 
Haversian canals of bone. A similar layer was prolonged into the 
pulp cavity, so as to line the dentine on its inner surface. This 
layer is apparently to be regarded as a modified form of vaso- 
dentine. 
The teeth in the adult mandible were formidable tusks, which 
curved up the sides of the beak on to its dorsum, where they decus- 
sated across the middle line. Each tooth was 14 inches long, 71- 
inches of which had protruded beyond the gum. It consisted of a 
triangular denticle and a strap-shaped curved shaft. The denticle 
was somewhat smaller than in the young tooth, and the enamel 
was almost entirely worn off its surface. The size of the tooth was 
therefore due to the enormous development of the fang which 
formed the strap-shaped shaft. The shaft consisted for the most 
part of a cortical layer of cement investing an opaque central band, 
which had the structure of the modified vaso-dentine of the younger 
tooth. 7-10ths of an inch from the summit of the shaft was a 
minute mesial chink 1-1 Oth inch long, which represented the pulp 
cavity, but the rest of the shaft was solid throughout. The summit 
of the shaft was more complicated in structure, and consisted from 
without inwards of the following layers : — cement, opaque modified 
vaso-dentine, opaque vaso-dentine, dentine, opaque modified vaso- 
dentine. When traced from the summit to the sides of the shaft 
the dentine and vaso-dentine disappeared, and then the two layers 
of modified vaso dentine blended with each other and formed the 
opaque central band of the rest of the shaft. The size of the fang 
is due to the great growth of the cement and the tissue of the 
opaque central band. The teeth of this specimen are larger than in 
any of the previously recorded specimens, and the animal from 
which they are obtained was probably an old male. 
The structure of the teeth of Mesoplodon Sowerbyii was examined 
from the skull described by the author in the “ Transactions of the 
Royal Society, Edinburgh,” 1872, vol xxvi. Each tooth was later- 
ally compressed, and formed almost an equilateral triangle, and the 
crown was not separated from the fang by any sharp line of demar- 
cation. The tooth consisted in great part of dentine, which in the 
crown was invested by a layer of not very strongly marked enamel. 
