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of the neck which are subjected to the pressure, while the central depressed part
is less affected. Accordingly the cartilaginous covering of the joint is spread
especially over the two lateral swellings of the neck; the depression between these
remains free (plate 95, fig. 3, b). But now the two swellings act very differently.
The medial swelling presents a direct continuation of the medial edge of the sur-
face of the trochlea, as we can see by taking a corresponding impression with
lead wire (fig. 495, e). The action of the lateral swelling is wholly different.
It rises sharply from the surface of the trochlea (fig. 495, f). Consequently, when
the foot is flexed in a dorsal direction, the medial swelling slides smoothly under
the articular surface of the tibia, without altering essentially the edge of the latter;
at most it deepens a little more the depression of the articular surface at the base
of the malleolus. On the other hand, the lateral swelling presses itself against
the edge of the articular surface, flattens it and produces the above-mentioned
overspreading of the cartilage on the anterior surface of the bone. If this explana-
tion is right, the edges of the cartilage-covered surfaces on the astragalus and
tibia must fit each other exactly, when brought into an extreme dorsiflexion.
Indeed that is so in our case. This, too, gives a certain proof that our astragalus
belongs really to the fragment of tibia.

That the squatting position gives rise to this strong dorsal flexion is shown
by the fact that the change just described on the lower joint is often accompanied
by a corresponding one on the upper joint. We find there often a rounding
off of the posterior edge of the joint-surface, which shows itself especially on the
lateral joint-groove and causes the joint-groove to appear convex in its posterior
segment. Also this characteristic is indicated on the left tibia head, even if
not very marked (fig. 495, a). It would correspond about to No. 2–3 of Thomson's
scheme (1890, p. 211). The cause of this variation is doubtless to be found in the
strong flexure of the knee, through which the posterior, upper surface of the
condyles is brought against the posterior edge of the joint-surface of the tibia.
It is at least doubtful whether the backward divergence of the head of the tibia
(plate 95, fig. 2) is also produced, or increased, by strong bending of the knee,
since it seems to occur in cases where such a function can not be shown as a cause.
An examination of this divergence by Manouvrier's method (1893, p. 231) gave
an angle of inclination of 10°. The angle of retroversion could not be measured;
with the considerable curvature of the tibia it is not possible to speak of a straight
diaphysis axis so that we have no criterion for the position. An inclination angle
of 10° lies perfectly within the range of variation of modern Europeans and exceeds
but little the average value, 8.5°, found by Manouvrier for 72 European tibiae
(French) (1893, p. 236). The described curvature of the thigh bone, as well as
of the tibia, by enlarging the space for the flexure muscles of the upper and lower
part of the leg, facilitates squatting; this is so self-evident that one might consider
whether this habit did not contribute to the increase of those curvatures.

Also the low position of the condylus medialis tibiae seems to be more common
among primitive peoples (plate 96, fig. 1).