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Show 1871. J MR. J. W. CLARK ON THE NARWHAL. 43 These authors have so thoroughly investigated the subject, that any value m y paper may possess will be due to the fact of its introducing their views to English readers. The skulls of the toothed Whales are generally asymmetrical, being twisted more or less, usually towards the left. This peculiarity is especially observable in Monodon. One would expect it to be greatly exaggerated in the skulls of the males, where the left tusk alone is developed, and the left maxillary is in consequence very large, and the right proportionately small. But it does not seem to be affected by the absence or presence of teeth. Female skulls, where neither tusk is developed, are equally twisted ; and so are the bidental skulls (fig. 1, p. 46), so far as I have been able to observe them, with the exception of the one at Amsterdam, which, if Vrolik's figure is correct, is twisted far less than any of the others. The increased size of the right maxillary does not appear to affect the rest of the skull. The normal dentition of the adult Narwhal is as follows :-In the male the left tusk alone is developed, while the right remains abortive in its alveolus. This closes over it so as to leave no external trace of the existence of a tooth within it. In the female both tusks remain abortive, like the right tusk in the male. The developed tusk measures usually, in an adult, about 98" in length (of which 14" are concealed within the alveolus), and is 8" in girth at the outer edge of the maxillary. It is spirally striated in a direction from right to left; and frequently the body of the tooth is twisted upon itself in a spiral*, the direction of which is also sinistral. There are generally five or six turns of the spiral, which become gradually further and further apart as they approach the tip of the tooth, extending to within 6" or 7" of the point in a tusk of average length. The extremity is without spiral markings. Scoresbyt notices that the striated portion is usually grey and dirty, the extremity clean and white ; and of one taken in his Greenland voyage he remarks'}:, " the tooth was covered, over the greater part of its surface, with a greasy substance, forming a blackish-brown incrustation. The underside of the horn, however, and a few inches of the point were quite clean, white, and polished." Anderson §, in a very graphic passage, compares the discoloured portion to the scabbard of a sword, so strong is the contrast between the grey and white portions. I have carefully compared m y bidental specimen with several normally developed Narwhal skulls in which the alveoli of the teeth have been laid open; and I find that the alveolus of the tooth or teeth is hollowed out in the maxillary alone, and in no other bone whatever. Hence Cuvier || is wrong in saying that the alveolus is * Three such are preserved in the Museum of the Eoyal College of Surgeons, Nos. 2535, 2536, 2540; and in almost every museum, or shop where Narwhal ivory is sold, tusks so twisted may be seen. It may therefore almost be regarded as a normal form. For the dentition given above see Owen, ' Odontography,' p. 348. f Arctic Regions, i. p. 490. J Greenland, p. 133. § Nachrichten von Giv inland, &C, p. 202. || Oss. Fossiles, v. pt, i. p. 322. |