(6 ) 
only cartilaginous cornea, three in number, which vary in com- 
plication ; it is very sensible, although it has not any sinus hol- 
lowed out in the thickness of the skull, (i) The width of the bony 
openings of the nostrils determines the form of the beak ; and 
the cartilages, the membranes, the feathers, and other teguments 
which narrow these openings, influence the strength of smell, and 
the kind of nourishment. 
The tongue has but little muscular substance, and is sustained 
by a prolongation of the os hyoidis. (2) 
The feathers as well as the pens, for they only differ in size, 
are composed of a stem (hollow at its base), and beards, which 
bear others still smaller; their texture, their brilliance, their 
strength, their general form, varies to infinity. The touch must 
be weak in all the parts which are covered with feathers; and as 
the beak is almost ahvays horny, and not very sensible, and the 
toes are covered with scales above and a callous skin below, this 
sense must be of very little efficacy in birds. 
The feathers fall twice every year. In certain species, the 
winter plumage differs from that of the summer; in the greater 
number, the female differs from the male by less lively colours, 
and then the young ones of both sexes resemble the female. When 
male and female adults are of the same colour, the young ones 
have a plumage peculiar to themselves. 
(1) In Mammalia^ these shiuses (which are distinguished from simple 
cavities by having a channel of communication with the seat of some 
organ) are covered^ as well as the cornea, with a soft membrane, upon 
which the branches of the olfactory nerves are distributed: their surface 
(against which the volatile particles of the effluvia of bodies strike after 
passing through the nose) is thus much more developed or spread, and 
consequently more susceptible. The tracing of the olfactory nerves to 
the palate, by Jacobson, satisfactorily accounts for the intimate sympathy 
between taste and smell. The projection of forehead in the Owl and 
the Elephant, which induced the ancients to attribute superior wisdom 
to them, is caused by the large cells between the interior and exterior 
sufaces of the frontal bone. In the Elephant they communicate with 
the nostrils, and are therefore true sinuses, which probably strengthen 
the sense of smelling ; but in the Owl they are simple insulated ca- 
vities. 
(2) See fig. 12, wherein c is the cartilaginous prolongation of the 
OS hyoidis, and t the upper part of the trachea^ the orifice of which is 
closed at the pleasure of the animal. Dumeril observes, that the organ 
of taste scarcely exists in Birds; that, in general, the j have no saliva, 
and swallow their food without mastication. There are some, how- 
ever, Parrots and Ducks, for instance, which appear to taste their food, 
and also possess the organs for furnishing saliva. 
