42 



independently of the projecting tusks, unerringly characterlzes tbe 

 skull of the malė Dugong. 



" It has been suggested tliatthe use of the projecting tusks in the 

 Dugong is to detach fuci from the rocks to -vvhich they adhere : 

 one can hardly, however, assign any important function in relation 

 to nutrition to parts which are limited to the malė sex ; but it mušt 

 be remembered that the function \vas assigned by a physiologist who 

 supposed that the tusks in question \vere specific and not sexual 

 characters, and that the imperfect tusks, whicli are peculiar to the 

 femalc, vvere the predecessors of the projecting tusks, and, in fact, 

 deciduous teeth. This opinion of Sir Everard Home was first called 

 in question by Dr. Knox*, who, having detected the suijposed de- 

 ciduous tusks in the head of a nearly full-gro\vn Dugong, rejected \vith 

 great justice the opinion of Home, that they are deciduous teeth ; 

 and he truly observes, that no evidence had been given to prove 

 the existence of deciduous tusks at all in the Dugongf. 



" I need hardly observe that the tusks of the Dugong, being im- 

 planted in the intermaxillary bones, are to be regarded, likę the tusks 

 of the Elephant, as incisors. Now both sexes of the Dugong, as of 

 the Elephant, do, in fact, possess deciduous or milk-tusks, but they 

 are much smaller than the female permanent tusks or supposed de- 

 ciduous teeth of Home. 



" In a recent cranium of a malė Dugong, sent to the Zoological 

 Society in spirits, I found in the upper jaw the deciduous incisors 

 or tusks coexisting ■vvith the permanent ones. They were loosely 

 lodged, by one extremity, in conical sockets immediately auterior to 

 those of the permanent tusks, and adhered by their ojjposite ends 

 to the integument, which externally presented no protuberance or 

 other indication of them. They ^vere tvv'o inches in length, slightly 

 curvcd, subcylindrical, tapering to both extremities, the fang-end 

 being the smallest, and perforated by an aperture leading to the ex- 

 tremely contracted cavity in which the remnant of the exhausted 

 matrix was lodged. From a comparison of the jaws of the dissected 

 specimens, and several crania of different ages, it appears that not 

 more than 20 grinders are developed in the Dugong, viz. 5 on each 

 side of each ja\v. Of these the first is shed before the lašt or fifth 

 comes into use. In the dry skull I have seen the lašt molar pro- 

 jecting from its socket, before either the deciduous incisor or the 

 iirst molar had been shed, but its crown presented the primitive 

 tuberculate apex, and had not penetrated the gum. The molares 

 increase very regularly in size from the first to the lašt. The fang 

 of the first and second is soon completed and solidified by the pro- 

 gressive absorption of the pulp : that of the third retains for a longer 

 period its pulp and expanded conical cavitj', but it becomes at length 

 contracted to a point, and is pushed out ; the fourth and fifth mo- 



* Edinb. Phi). Trans. xi. p. 389. 



t " The milk-tusks of the Dugong have never been seen by any one ; 

 that is, I have not heard of the existence of any preparation shovving the 

 germs of the milk or permanent teeth, together or in succession." — Dr. 

 Knox, loc. cit, p. 398. 



