149 
and organs of hearing of the dugong. 
tusks of the dugong, show that the milk tusks have been 
mistaken for the permanent ones, and that the real appearance 
of the permanent tusks of this animal is at present unknown. 
Having corrected so great an error in the natural history of 
this animal, we must wait till we are so fortunate as to pro- 
cure the skull of a full grown dugong, before we attempt to 
form any analogies between its tusks and those of other 
tribes of animals. 
The grinding teeth, as will be seen in the annexed plate, 
are not exactly similar to those of any known animal, but 
form an approach to the hippopotamus. They consist of 
two cones united together ; but when a transverse section is 
made, there is no line of separation, the whole being uniform ; 
the external crust is not enamel, nor is it the hardest part ; a 
little within it, there is a narrow rim of a yellow colour, that 
describes an oval figure, much more dense than the rest of 
the tooth, although to the eye there is no apparent difference 
in its texture ; all that is within this rim is soft ivory ; so that 
these teeth in wearing down will always have the crown 
rendered concave. 
On the organ of hearing. 
In examining the organ of hearing of the dugong, which 
was done with more facility, as the skull had not been com- 
pletely formed, I met with a peculiarity, that does not belong, 
as far as I am aware, to any other tribe of animals. The 
malleus and incus, which have nearly the same shape as in 
other animals, are fastened to the sides of the tympanum by a 
bony substance extending across the intervening space. The 
malleus is in this way connected to one side of the tympanum, 
X 
MDCCCXX. 
