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The muscles which move the tibia, and indirectly the femur, also consist of an extensor muscle which is situated in the upper side of the femur (Fig. 116, s, Fig. 115, f), and of a flexor (Fig. 116, b, Fig. 115, g), which lies under the former.

The stilt-like spines on the point (Figs. 115 and 118, L3n) on which this segment is directly supported are important parts of the tibia. (Graber.)

Fig. 117.—Left fore leg of a cerambycid beetle: h, coxa; r, trochanter; o, femur; u, tibia; f, tarsus; k, claw.—After Graber.

Considering the respective positions of the individual levers of the leg and the nature of the materials of which they are made, the legs of insects may be likened, as Graber states, to elastic bows, which, when pressed down together from above, their own indwelling elasticity is able to raise again and thus keep the body upright.

This is very plainly shown in certain stilt-legged bark-beetles, in which, as in a rubber doll, as soon as the body is pressed down on the ground, the organs of motion extend again without the intervention of muscles; indeed this experiment succeeds even with dead, but not yet wholly stiff, insects.