220 AVES) §,, ke. ie 
able muscular apparatus, can be drawn over the eye like a 
curtain. The cornea is very convex, but the crystalline i is 
flat, and the vitreous humour small. oF 
The ear has but a single small bone, formed of one branch 
that adheres to the tympanum, and of another terminating in 
a plate that rests upon the fenestra ovalis; the cochlea is a 
slightly arcuated cone; but the semi-circular canals are 
large, and lodged in a part of the cranium where they are 
completely surrounded by air cavities, which communicate. 
with the arca. Nocturnal Birds alone have a long external” 
conch, which, however, does not project like that of Quadru- 
peds. The external meatus is generally covered with feathers, 
whose barbs are more fringed than the others. 
The organ of smell, concealed in the base of the beak, usu- 
ally has but three cartilaginous ossa turbinata, which vary in 
complication ; although there are no sinuses within the pari- 
etes of the cranium, it is extremely sensible. The breadth of 
the osseous openings of the nostrils determines the strength of 
the beak; and the cartilages, membranes, feathers and other 
teguments which narrow down those apertures, influence the 
power of smell, and the nature of the food. 3 
There is but little muscular substance in the tongue, which 
is supported by a bone articulated with the hyoid ; in most 
Birds this organ is not very delicate. 
The feathers, as well as the quills, which only differ in size, 
are composed of a stem, hollow at base, and of barbs, which 
are themselves furnished with smaller owes ; their tissue, lustre, 
strength, and general form vary infinitely. The touch must if 
be feeble in all such parts.as are covered with them, and as 
the beak is almost always corneous, and has but little sensi- 
bility, and the toes are invested with scales above, and a callous” 
skin underneath, that sense can have but little activity in this 
class of animals. 
Birds moult twice a year. In certain species, the winter 
plumage differs in its colours from that of summer; in the 
greater number, the female differs from the male in an infe- 
rior vividness of tints, and when this is the case, the young of 
