350 CETACEANS. 



inches in length, and exposed by the laying open of the narrow socket 

 (' rima'), in which it was lodged. Two very accurate views of this abor- 

 tive tusk are given in the figures 23 and 24 of the Plate which illustrates 

 the paper, and the Author conjectures that it may serve to supply the 

 place of the large left tusk should this be either broken away by violence, 

 or shed naturally in process of time. The normal tusk in the skull of the 

 Narwhal, ' Cete NarhuaV the subject of his observation, was inserted 

 fourteen inches deep, and projected nearly four feet from the socket, 

 but its extremity had been broken off. It is figured in the Plate, together 

 with two views of the skull from which the tusks are removed, 

 the fissure, or alveolus of the abortive tusk being shown in Fig. 21. 

 The plate bears no number, but is marked p. 35. I doubt whether 

 Cuvier had ever read this paper : it has the priority of Tichonius' 

 often cited Dissertation " Monoceros piscis baud monoceros," by four 

 years, having been printed in 1702. 



The skull of a Narwhal, with two long exserted tusks, formed 

 part of the collection of the late Joshua Brookes ; in this specimen 

 the alveolus of the right tusk appeared to have been artificially 

 enlarged, and the tusk was unquestionably cemented in its place ; but 

 the circumstance which most militated against its authenticity was 

 the direction of the spiral lines which corresponded with, instead of 

 opposing those of the left tusk. 



With regard to the conjectured ulterior use of the concealed tusk 

 in the male as a substitute in the event of the loss of the large tusk 

 — a conjecture more than once repeated since first proposed by Reisel, 

 — the solidity of the concealed tusk and its distorted and generally 

 closed base evince that the term of its growth has expired. 



142. DelphinidfJB. In the Delphinus griseus the dentition of the 

 upper jaw is transitory as in the Hyperoodon, but at least six 

 pairs of teeth rise above the gum, and acquire a full development 

 at the fore-part of the lower jaw : the crowns of these teeth soon 

 become obtuse ; and even their duration is limited, for the specimen 

 described by M. F. Cuvier(l) had but two teeth on each side of the 

 lower jaw. A Dolphin, perhaps an aged individual of this species, 

 has lately been described with the dentition reduced to two teeth 

 (1) Dents de Mammiferes, p. 243. It was eleven feet in length, and captured at Brest. 



