The author expressed his concurrence with those anatomists who hold that the two tusks of the narwhal are situated in sockets in the superior maxillary bones, and not, as was stated by the Cuviers, in the premaxillæ, or partly in the pre- and partly in the superior maxillæ. He then proceeded to relate some further observations on the dentition of the narwhal, and pointed out, both in the skull of a young male and in those of three well grown fœtuses, an elongated canal on each side of the upper jaw, parallel and inferior to the tusk socket, which had the appearance of a socket for a supplementary tooth, although none protruded from it. In the young male a minute denticle was seen at the bottom of this socket.