COMPARATIVE ANATOMY. 
by the feet ; and lastly, That the feet them- 
selves should have a broad surface resting 
firmly on the ground, and should admit of 
being in a manner fixed to the earth. All 
these circumstances are united in the ne- 
cessary degree in man only. 
The broader the surface included by the 
feet, the more securely vrill the line of gra- 
vity rest within that surface. The feet of 
man are much broader than those of any 
animal, and admit of being separated more 
vridely from each other. The sources of 
the latter prerogative reside in the superior 
breadth of the human pelvis, and in the 
length and obliquity of the neck of the fe- 
mur, which, by throwing the body of the 
bone outwards, disengage it from the hip- 
joint. 
Tlie whole tarsus, metatarsus, and toes, 
rest on the ground in the human subject, 
but not in other animals. The simiae, and 
the bear, have the end of the os calcis raised 
from the surface ; while, on the contrary, 
it projects in man, and its prominent por- 
tion has a most important share in support- 
ing the back of the foot. Tlie exterior 
margin of the foot rests chiefly on the 
ground in the simiae ; which circumstance 
leaves them a freer use of their thumb and 
long toes in seizing the branches of trees, 
&c.; and renders the organ so much the 
less adapted to support the body on level 
ground. 
The plantaris muscle, instead of termi- 
nating in the os calcis, expands into the 
plantar fascia in the simiae; and in other 
quadrupeds it holds the place of the flexor 
brevis or perforates digitornm pedis, pass- 
ing over the os calcis in such a direction 
that its tendon would be compressed, and 
its action impeded, if the heel rested on the 
ground. 
The extensors of the ancle joint, and 
chiefly those which form the calf of the 
leg, are very small in the mammalia, even 
in the genus simia. The peculiar mode of 
progi-ession of the human subject sufficiently 
accounts for their vastly superior magnitude 
in man. By elevating the os calcis they 
raise the whole body in the act of progres- 
sion; and, by extending tlie leg on the foot, 
they counteract that tendency which the 
weight of the body has to bend the leg in 
standing. 
The thigh is placed in the same line with 
the tmnk in man ; it always forms an angle 
with the spine in animals, and this is often 
even an acute one. The extensors of the 
knee are much stronger in the human sub- 
ject than in other mammalia, as their dou- 
ble effect of extending the leg on the thigh, 
and of bringing the thigh forwards on the 
leg, forms a very essential part in the hu- 
man mode of progression, 
The flexors of the knee are, on the con- 
trary, stronger in animals, and are inserted 
so much lower down in the tibia (even in 
the simiae) than in the human subject, that 
the support of the body on the hind legs 
must be very insecure, as the thigh and leg 
form an angle, instead of continuing in a 
straight line. 
The gluteus maximus, which is the largest 
muscle of the human body, is so small and 
insignificant in animals, that it may almost 
be said not to exist. This muscle, which 
forms the great bulk of the human buttock, 
extends the pelvis on the thighs in stand- 
ing ; and, assisted by the other two glutei, 
maintains that part in a state of equilibrium 
on the lower extremity, which rests on the 
ground, while the other is carried forwards 
in progression. The true office of these im- 
portant muscles does not therefore consist, 
as it is usually represented, in the common 
anatomical works, in moving the tliigh on 
the pelvis, but in that of fixing the pelvis on 
the thighs, and of maintaining it in the 
erect position. 
Such tlien are the supports, by which the 
trunk of the human body is firmly main- 
tained in the erect position. The proper- 
ties of the trunk, which contribute to the 
same end, do not so immediately belong 
to this article; but may be slightly men- 
tioned to complete the view of the 
subject. The breadth of the human pelvis 
affords a firm basis on which all the superior 
parts rest securely; the same part is so 
narrow, in other animals, tliat the trunk 
represents an inverted pyramid, and tliere 
must consequently be great difficulty in 
maintaining it in a state of equilibrium, if 
it were possible for the animal to assume 
the erect position. In those instances 
where the pelvis is broader, the other con- 
ditions of the upright stature are absent : 
the bear, however, forms an exception to 
this observation, and consequently admits 
of being taught to stand and walk erect, 
although the posture is manifestly inconve- 
nient and irksome to the animal. 
The perpendicular position of the verte- 
bral column under the centre of the basis 
cranii, and the direction of the eyes and 
mouth forwards would be as inconvenient 
to man, if he went on all-fours ; as they are 
well a^pted to his erect stature. In the 
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