1871] MR. J. W. CLARK ON THE NARWHAL. -43 



These authors have so thoroughly investigated the subject, that any 

 value my 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 abor- 

 tive 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, ex- 

 tending to within 6" or 7" of the point in a tusk of average length. 

 The extremity is without spiral markings. Scoresbyf 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 un- 

 derside 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 my bidental specimen with several nor- 

 mally 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 giren above see Owen, ' Odontography,' 

 p. 348. 



f Arctic Eegions, i. p. 41J0. 



X Greenland, p. 133. 



§ Nachrichten von GWmland. &c., p. 202. 



|| Oss. Fossiles, v. pt. i. p. 322. 



