42 



independently of the projecting tusks, unerringly characterizes the 

 skull of the male Dugong. 



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

 Dugong is to detach fuci from the rocks to which they adhere : 

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

 to nutrition to parts which are limited to the male sex ; but it must 

 be remembered that the function was assigned by a physiologist who 

 supposed that the tusks in question were specific and not sexual 

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

 female, were 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 supposed de- 

 ciduous tusks in the head of a nearly full-grown Dugong, rejected with 

 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, like 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 male Dugong, sent to the Zoological 

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

 or tusks coexisting with the permanent ones. They were loosely 

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

 those of tlie permanent tusks, and adhered by their opposite ends 

 to the integument, which externally presented no protuberance or 

 other indication of them. They were two inches in length, sUghtly 

 curved, subcjdindrical, 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 jaw. Of these the first is shed before the last or fifth 

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

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

 first 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 last. 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 cavity, but it becomes at length 

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



* Edinb. Phil. Trans, xi. p. 389. 



f " The milk-tusks of the Dugong have never been seen b)' any one ; 

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

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

 Knox, loc. cit. p. 398. 



