THE ORNITHORHYNCHUS PARADOXUS. 231 
great expansion. The claws on the fore feet are strong, blunt, and well calculated for 
burrowing ; and the two lateral are shorter than the three middle ones. The hind feet 
are short, narrow, turned backwards, and when the animal is at rest have, like those 
of the Seal, some resemblance to a fin ; their action is backwards and outwards. The 
first toe is very short, and the nails of all are curved backwards, and are longer and 
sharper than those of the fore feet ; the web does not extend further than the roots of 
the claws. The spur of the male is moveable, and is turned backwards and inwards : it 
is situated some distance above the claws, and rather towards the internal part of the leg. 
The head is rather flat; and from the mouth project two flat lips or mandibles, re- 
sembling the beak of a Shoveller Duck, the lower of which is shorter and narrower 
than the upper, and has its internal edges channelled with numerous strié, resembling 
in some degree those seen in the bill of a Duck. The central portion of the mandibles 
is a bony continuation from the skull, and anteriorly and laterally a cartilaginous 
substance, perfectly moveable, extends from the bony portion to the distance of 3ths 
of an inch. The colour of the Superior mandible above, when seen in an animal 
recently taken out of the water, is of a dull dirty greyish black, covered with innu- 
merable minute dots; while the cartilaginous expansion around the mandible is uni- 
formly smooth and soft. The under part of the upper mandible is of a pale pink or 
flesh colour, as well as the internal or upper surface of the lower mandible, the under 
surface of which is either perfectly white or mottled: in younger specimens it is usually 
white, while in the older it assumes a mottled appearance. 
At the base of both the lower and upper mandibles is a transverse loose fold or flap 
of the integument, always similar in colour to the skin covering the mandibles, that 
is to say, of a dull dirty greyish black in the upper, and white or mottled in the lower. 
In the upper mandible this is continued very nearly to the eyes, and may perhaps afford 
Some protection to those organs when the animal is engaged in burrowing or seeking 
its food in the mud. The upper fold or flap is continuous with another portion arising 
from the lower mandible also at its base. Sir Everard Home! considers the apparent 
use of these folds to be to prevent the beak from being pushed into the soft mud beyond 
this part, which is so broad as completely to stop its further progress. From careful 
observation of the actions of living specimens I can, however, assign no other use to 
this part than that which I have just mentioned. In dried specimens the colour and 
form of the beak are almost entirely lost. 
The eyes are very small, but brilliant, and of a light brown colour: they are situated 
rather high up the head. The external orifice of the ears is situated near the upper 
part of the external angle of the eye. When a living specimen is examined the 
orifice? is easily discoverable, as the animal has the faculty of closing or opening it at 
‘ Observations on the Head of the Ornithorhynchus paradocus, in the ‘ Philosophical Transactions’ for 1800. 
* I could not perceive any valve corresponding to that which is usually possessed by animals that frequent 
the water, but believe that the muscular contraction of the orifice answers the same purpose. 
