. Animal locomotion or walking, swimming, and flying : with a dissertation on aëronautics. and the legs to the pelvis (a, a), as a knowledge ofthese is necessary to a comprehension of the oscillating orpendulum movements of the limbs now to be described. Thescrew configuration of the limbs is well depicted in the leftarm (x) of the present figure. Compare with the wing of thebird, fig. 6, and with the anterior extremity of the elephant,fig. 7, p. 28. But for the ball-and-socket joints, and thespiral nature of the bones and articular surfaces of the extre-mities, the undulating, sinuous, and mo
. Animal locomotion or walking, swimming, and flying : with a dissertation on aëronautics. and the legs to the pelvis (a, a), as a knowledge ofthese is necessary to a comprehension of the oscillating orpendulum movements of the limbs now to be described. Thescrew configuration of the limbs is well depicted in the leftarm (x) of the present figure. Compare with the wing of thebird, fig. 6, and with the anterior extremity of the elephant,fig. 7, p. 28. But for the ball-and-socket joints, and thespiral nature of the bones and articular surfaces of the extre-mities, the undulating, sinuous, and more or less continuousmovements observable in walking and running, and thetwisting, lashing, flail-like movements necessary to swimmingand flying, would be impossible. The leg in the human subject moves by three joints, viz.,the hip, knee, and ankle joints. When standing in the erectposition, the hip-joint only permits the limb to move forwards, PROGRESSION OX THE LAND. 55 the knee-joint backwards, and the ankle-joint neither back-wards nor forwards. When the body or limbs are inclined. Fig. 26.—Skeleton of Man. Compare with fig. 4, p. 21, and fig. 24, p. 47.—Original. obliquely, or slightly flexed, the range of motion is increased. 5G ANIMAL LOCOMOTION. The greatest angle made at the knee-joint is equal to thesums of the angles made by the hip and ankle joints whenthese joints are simultaneously flexed, and when the angle ofinclination made by the foot with the ground equals 30°. From this it follows that the trunk maintains its erectposition during the extension and flexion of the limbs. Thestep in walking was divided by Borelli into two periods, theone corresponding to the time when both limbs are on theground; the other when only one limb is on the ground. Inrunning, there is a brief period when both limbs are off theground. In walking, the body is alternately supported bythe right and left legs, and advanced by a sinuous forward motion is quickened when o
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