302 
LECTURES ON HOUSES. 
were it not for the super-imposition of the patella, the front of the 
joint would be left dangerously insecure and entirely unprotected. 
The Patella, or stifle-bone, of the horse, corresponds to the 
patella or knee-pan of a man : their anatomical situation and 
relations are the same, and they answer similar purposes in both 
animal machines. However irreconcileable with any notions of 
relative situation it may at first appear to an unprofessional mind, 
the stifle of the horse is regarded by the human anatomist as his 
knee , for the same reason that the veterinarian would look upon 
the knee of a man as his stifle. One grand difference, however, 
between these structures is, that, in man the femoral bone stands 
perpendicularly upon the tibia, whereas, in the quadruped the 
bones are placed at a right angle, almost, in regard to each other : 
a circumstance from which we may infer that the patella was not 
added for the purpose of making the joint complete so much as 
for the grand object of serving as a pulley and a lever to the 
muscles engaged in the important business of extending the thigh 
under the body and aiding in progression. The biped — man — is 
enabled to maintain his erect posture with comparative ease, or at 
little expense of muscular action, by means, principally, of large 
and powerful muscles inserted into his knee-pan : were the knees 
not kept straightened the stability and strength of the standing 
posture would be lost : when from weakness, or any other cause, 
the extensor muscles lose part of their power, so that the legs 
cannot be completely straightened, we know how insecure the 
standing is, to say nothing of the awkwardness and infirmness it 
occasions in progression. Even after a man has had fracture of 
one of his knee-pans, and the fractured divisions of bone have 
united — as they commonly do through the intervention of liga- 
mentous substance — the increased length of the pulley and conse- 
quent diminished effect resulting from the contractions of the ex- 
tensor muscles, occasions halting in the walk, and detracts from 
the stability of the standing posture. To the quadruped these 
observations are not altogether strictly applicable. Standing, as 
he does, upon four legs, and these being so placed that the body is 
mechanically supported by them, after the manner of a stool or 
form upon its four supporters, but very little muscular action is 
necessary to keep him standing ; and although the muscles affixed 
to the patella contribute to this function, yet is that office com- 
paratively trifling to the one they perform in the work of pro- 
gression. When the hind limbs, through the agency of the flexor 
muscles, have been raised or flexed to their utmost, then do the 
extensor muscles come into play, projecting the limbs underneath 
the body, and pointing the toes forward, in order that they may 
