( 4 ) 
The bony tail is very short, but it also bears a row of strong; 
pens, which, by spreading, contribute to the support of the bird'; 
their number is generally twelve, sometimes fourteen, and, in the 
Gallinacew, even as many as eighteen. 
The legs have a femur, a tibia, and a peronaeum or fibula, con- 
nected with the femur by an elastic ligament, by means of which 
the extension is maintained without any effort on the part of the 
muscles, (i) The tarsus and metatarsus are represented by a 
single bone, terminating, towards the base, in three pullies. 
There are most frequently three toes in front, and a great toe 
behind; the latter is sometimes wanting. The great toe is directed 
forwards in the Martins. In the Scansores (Climbers ) the last 
as well as the great toe is directed backwards. The number of 
articulations or joints increases at every toe, beginning with the 
great toe, which has two; and ending with the last toe, which has 
five. (2) 
Birds are generally covered with feathers, the species of tegu- 
ment best adapted to defend them from the rapid variations of 
of the bird; and are particularly developed in the Alauda (Merops), 
hanging down ])etween the body and the wing. The bastards form 
what is sometimes called the alula ; they are strong feathers, or pens, 
situated in the upper end of the under surface of the wing, and very 
much developed in the Genus Falco. The tectrices inferiores are 
soft feathers between the bastards and the body. The feathers of the 
tail (which also has its tectrices superiores and inferiores) are called 
rectrices^ from being compared to a helm. 
(1) I have attempted to render this clear by the figures 7, 8 and 
9. In fig. 7, the ligament is in the relaxed state in which it rests when 
the femur and tibia are nearly perpendicular, or at least form a very 
obtuse angle \ ?• is a small rise or swelling in that part of the bone, in 
passing over which the ligament is compelled to strain or lengthen 
itself, as in fig. 8 ; directly it has passed this swelling, the strain ceases, 
and it instantly contracts, resuming the same state as at first, but on the 
contrary side of the swelling, as in fig. 9. Thus the peculiar jirk in 
the walk of Birds, particularly in the Grallce, is explained ; the exer- 
tion of the muscles raises the leg and foot from the ground, until the 
femur and tibia form the angle which strains the ligament to the 
utmost, as in fig. 8; and^the sudden contraction of this ligament spon- 
taneously raises the foot with a catch or jerk, as much higher from the 
ground as the gait of the bird requires ; in setting the foot to the 
ground in order to raise the other, the muscles are again called upon 
to act, until the ligament has resumed the position of fig. 8, its sub- 
sequent and sudden release and contraction replacing the foot on the 
ground as at first. 
(2) This is also the case with Reptiles; in Mammalia there arc 
always an equal number of joints to each toe. 
