412 DR KNOX on the Dentition of the Dugong, and on the 



and does actually become, partially divided into a number of 

 compartments by osseous division or ridges *. 



It is, moreover, probable that the inferior dentar canal, 

 which more resembles a great cavity, contains numerous blood- 

 vessels and nerves, calculated to allow of, and supply, the waste 

 of the jaw, and the succession and loss of teeth ; and the same 

 structure may prevail even in the narwal, since being of an 

 analogous nature with the other Cetacea, the jaws may waste 

 away in it although there be no teeth present, with the excep- 

 tion of the left tusk and the aborted tooth f of the right side. 



Since the period of the earliest voyages to the Arctic Seas, 

 the narwal, from the remarkable projecting and single tooth, 

 carried in the upper jaw, has attracted the attention even of 

 those least interested in zoological inquiries. The facts, that it 

 is the left tooth only which is developed in general that some- 

 times the right is also found to extend, more or less, beyond the 

 gums, but more usually remains in the socket, imbedded in the 

 jaw, probably for the whole life of the animal and that, in the 

 female, both these teeth remain in the jaw, and never shew 

 themselves external to the gums ; these are facts known to 

 every one. But I do not believe that these aborted teeth, 

 which remain imbedded in the jaw, viz. the right tooth in the 

 male and both in the female, are milk tusks, or merely tempo- 

 rary teeth ; neither is there a single observation in the history 

 of the narwal to shew that there really exists any true succes- 



* There is a species of Rhinoceros in which two incisive teeth remain below the 

 gum during the whole period of the natural life of the animal : they are not to be 

 seen then so long as the head is covered with soft parts. Thus the permanent 

 residence of teeth within the alveolar cavities, or not visible beyond the gums, as 

 assuredly happens in the narwal, and, as I supposed, might also occur in the case 

 of the lower incisives in the dugong, is a fact not confined to the Cetacea. 



f- An expression employed by M. CUVIEE. 



