- 
458 
second only backwards, and the third neither 
backwards nor forwards. 
The length of the legs, measured from the 
hip-joint to the ground when standing erect, 
preponderates slightly over that of the body 
when taken from the distance of the crown of 
the head to the axis of the hip joint, conse- 
quently the centre of gravity is raised above the 
plane of position rather higher than the semi- 
distance from the head to the ground when the 
entire sole of the foot is in contact with the 
earth.* In consequence of the lengths of the 
femur and tibia being nearly equal, and of the 
zigzag direction which the limbs take during 
flexion, and because the angle of the greatest 
flexion of the knee-joint is nearly equal to the 
sum of the angles of the hip and ankle, it 
results that in the simultaneous flexion of 
these three joints, (provided the angle of in- 
clination of the foot to the ground continues 
30°,) the trunk preserves its erect position as 
when standing, and therefore ascends and de- 
scends (by the flexion and extension of the legs) 
in the same vertical line. The greatest amount 
of elongation and contraction of the leg result- 
ing from the greatest extension and flexion of 
the hip, knee, and ankle-joints, may be easily 
ascertained by measuring with a line from the 
hip-joint to the head of the astragalus during 
such flexion and extension, and marking the 
difference in the length of the line in the two 
states. By this method the length is estimated 
by Weber as follows : 
m.m. 
In the greatest state of extension.. 924.26 
In the greatest state of flexion.... 404.74 
The actual lengths of the several portions of 
the leg are 
m.m. 
Head of the femur to the condyles. . 380.0 
From the condyles to the convex 
articular surface of astragalus .. 
Axis of articulation of the astragalus 
to centre of foot 136.0 
During the greatest extension the first three 
of these points of the leg formed an angle of 
148°8', and during the greatest flexion an angle 
of 40°. The second, third, and fourth points 
form in the greatest extension an angle of 
157° 4, and in greatest flexion 94° 6’. 
The proportion between the greatest and 
smallest length which the leg can assume varies 
but little. 
Figs. 247 and 248 from Weber show the 
greatest amount of extension and flexion which 
the leg can effect; the corresponding difference 
in length is as 14 to 5, but in walking and run- 
ning the flexion is less, and the difference of 
length as 11 to 9. 
In standing, the weight of the body is trans- 
mitted from the pelvis to the heads of the 
femurs; the oblique directions of the latter 
upwards and inwards keep in equilibrio the 
vertical forces downwards and outwards pro- 
duced by the weight of the body on the wedge- 
like sacrum. 
The femurs transmit the weight impressed 
420.0 
* See positions of the centre of gravity, sect. i, 
p. 409. 
MOTION, 
Fig. 247. 
on them by the trunk, together with their own 
weight and that of the soft parts to the tibie. 
The shafts of the latter are straight, and by thei 
rismatic form their solid contents are ver 
urther from the axis of the bone, which enable: 
them to support a greater weight with less ex- 
penditure of materials. 4 
The fibula adds likewise to the strength ¢ 
the tibia, both vertically and laterally; the 
latter transmits, in its turn, its own weight at 
that of its soft parts to the astragalus. 
The astragalus transmits the pressure made 
upon it partly to the calcaneum and partly 1 
the scaphoides; the calcaneum partly to t 
ground and partly to the cuboides; the se 
phoides transfers the force through the cune 
form bones; the toes to the ground, whe 
the base of support terminates, supposin 
the entire foot to rest on it. In the mechanist 
of the foot we discover an elastic arch, up¢ 
which the shock of the body is received, ar 
transmitted obliquely to the ground. This adm 
rable structure prevents the jar which the bor 
would otherwise sustain at each step by thes 
action of the ground in walking, running, le: 
ing, or falling; but an exact investigation 
the mechanism of the foot would occupy mi 
space than we have assigned to this subj 
The areas of the soles of the two feet and © 
space lying between them is the whole base 
support in standing on both legs; but w 
standing upon one only, this is diminish 
not only by the area of one foot, but also o 
space lying between them. In the latter: 
the base is so narrow that the act is not easi 
complished, but the difficulty of keep 
trunk in equilibrium is vastly increase 
the base of support is reduced to the area 0 
great toe, as is accomplished by opera dani 
or to the area of one-fifth or two-fifths 
square inch as in skating, or to one still le 
in rope dancing, wherein the base of sup 
oscillates laterally. In this latter case, the ¢ 
culty is increased by the necessity of keeping 
trunk in equilibrio, but the centre of gravi 
retained in the plane of the rope by ixin 
eye on some distant point in it. The- 
tion which the two feet ought to take, ¥ 
equally advanced and equally inclined, so 
Pili 
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