Anatomical Structure of certain of the Cetacea. 393 



I had thus before me the crania of two adult specimens of 

 the dugong, for such I presumed them to be, one prepared by 

 myself, and one by some persons abroad. A little dissection 

 brought to light a most unexpected fact, viz. that the tusks of the 

 crania before me differed from each other in shape and general 

 appearance ; and that, whilst one of these resembled in all re- 

 spects the tusk which Sir EVERARD HOME had characterised as 

 belonging to the adult or complete animal, the other resem- 

 bled entirely the tusk which he considered as a milk-tusk. 

 Here, then, were two crania, evidently adult, possessing dif- 

 ferently formed tusks, which difference in form could not pos- 

 sibly depend on age, as had been advanced by Sir E. HOME, 

 but must depend on some other cause. Before we consider what 

 that cause may be, 1 shall take the liberty of briefly and rapidly 

 reviewing what has been done as to the anatomy of the dugong, 

 by those anatomists who have preceded me in this inquiry, 

 stating in the first place, succinctly and briefly, those facts (and 

 the conclusions drawn from them by myself), which may be veri- 

 fied by the Members of this Society and by others, by simply 

 inspecting the two crania, I have had an opportunity of describ- 

 ing. 



The cranium of the skeleton at present in the possession of 

 the University, is somewhat smaller than that now before the 

 Society. The length of the skeleton is fully 7 feet 3 inches 

 English ; the bones are extremely hard, and the head dense and 

 heavy. In the crania I observed differences as to the shape of 

 various bones, when compared with each other, which, upon the 

 whole, however, hardly amounted to what I should venture to 

 call specific differences. They do not exactly resemble each 

 other. In the upper jaw there are two tusks in the intermaxil- 

 lary bones, and three molar teeth on each side, opposed to those 

 occupying a similar situation in the lower jaw-bone. The ante- 



