THE EXTREMITIES. 313 
which the limb itself is composed being bent at various angles, are pre- 
vented from giving way by the muscular actions of the extensors of the 
humerus and ulna, the carpus (or knee) having little tendency to yield, 
and the pastern being supported by the flexor muscles and suspensory 
ligament. The hinder hmbs, though sustaining less weight, are not so 
favourably circumstanced for this purpose, the angles between their 
several parts being generally more acute. But if these are attentively 
regarded, there is not so much difference as is generally supposed. Thus, 
the first joint, the ilio-femoral, forms a less acute angle than its analogue, 
the shoulder joint (see fig. 1, R.m). Again, though the stifle joint is con- 
siderably bent, it is not more so than the elbow joint, which will be clear 
on comparing the two in the skeleton given at page 308. ‘The chief dis- 
advantage sustained by the hind limbs as means of support will be found 
in the hock, as compared with the knee, the latter being nearly straight, 
while the former is much bent; but as it has a long lever to assist it (the 
os calcis), and as this is kept in position by the powerful hamstring 
muscles, each of which serves its purpose far more completely than the 
flexor of the carpus inserted in the os pisiforme, it may readily be under- 
stood that the hind limb is not greatly at a disadvantage in supporting 
the weight of the body. 
AS AGENTS OF LOCOMOTION, the offices of the fore and hind limbs are 
widely different. Each has been already described as consisting of four 
sections, bent at angles on each other. In the fore limb these angles are 
framed to serve as springs, so that when the feet touch the ground, they 
are enabled to adapt themselves so as to avoid altering the line of progres- 
sion of the body. In those animals which have small and short fore legs, 
as the kangaroo and hare, the most rapid locomotion ever consists in a 
series of curves; whereas, in the horse at full speed, the body progresses 
in one straight line, owing to this elastic structure of the anterior hmbs. 
So, also, in descending from an extraordinary leap, the springy action of 
the fore limbs of the horse is so powerful that he can get off again without 
dwelling, whereas the kangaroo and hare must depend almost entirely 
upon their hind legs, and consequently stop for a second after their descent. 
On the other hand, the angular formation of the hind limbs is intended 
to enable the animal to drive its whole body forward, by first flexing all 
the joints, and thus drawing the feet under the belly; and then suddenly 
extending them with the feet fixed in the ground, the weight is neces- 
sarily propelled. Or if the feet are not fixed they are lashed out back- 
wards, developing the action so well known as “kicking.” The difference 
between the powers displayed by the two limbs, in straightening their 
component parts, is well displayed in comparing kicking with the striking 
out of the fore foot, which is common enough among vicious horses. It is 
true that the latter will sometimes cause a severe blow; but it could very 
rarely break a limb, which is the least amount of mischief to be appre- 
bended from the full force of a lash out with the hinder limb. 
