LECTURES ON HORSES. 
183 
length is given : a horse with long femoral bones will be enabled 
in action to throw his hind feet farther forward than another with 
short ones ; that motion in the hip-joint which will advance the 
short bone as equal to three will project the long one as equal to 
four. 
I said the hip-joint was of the ball and-socket character, and 
therefore it possesses, to a greater or less extent, a rotatory mo- 
tion. Through its means it is that the animal has the power of 
“ tucking his haunches in,” or placing his hind foot centrically 
underneath his body, in the position, of all others, the most effec- 
tive for the propulsion of the machine in action : unless from the 
breadth and position of the pelvis, and the connexion with it, and 
conformation of the hind limbs, he derive this power from the 
hip joint, from no other joint, from want of the rotatory power, can 
such action proceed. It is quite a mistake to suppose that such 
“ tucking in” can be produced by the hocks, they admitting but of 
simple flexion and extension. Both the fore and hind extremities 
derive what faculty of lateral and rotatory motion they possess — 
the power of throwing the legs, and turning the toes inward or 
outward in action — from ball-and-socket joints : the fore extremity 
from the shoulder joint, the hind extremity from the hip joint. 
There is this important difference, however, in the construction of 
these correspondent articulations : the os humeri is placed beneath 
the scapula, in such a situation that the weight of the body comes 
directly upon its head; whereas, in consequence of the head or 
articulatory part of the os femoris, instead of forming the top of 
the bone, being laterally placed at a right angle to the shaft of the 
bone, the weight is transmitted, not directly upon the os femoris, 
but in an oblique or indirect line. One reason for this appears 
evident, in the different relations to the body existing between the 
shoulder and hip joints, the latter being in immediate connexion 
with the body itself, the former attached only through the interven- 
tion of muscle. The lateral position of the hip joint serves, in a 
measure, to compensate for the want of that elasticity and spring 
which the shoulder derives from its muscular attachments, to coun- 
teract or mitigate any shock or concussion the limb may sustain in 
action, such as from jumping, &c. There is another and a greater 
advantage, however, resulting from this position of obliquity. At 
the time that the weight of the body is pressing with its greatest 
force upon the hip joints, from the pressure being sideways instead 
of perpendicular, their motions under the weight are, compara- 
tively, easily carried on — the work of progression is saved that 
hinderance and difficulty which would have attended the direct 
imposition of weight upon these joints, to say nothing about the 
friction and wear from concussion, the joints themselves must 
