176 SPECIAL PHYSIOLOGY. 



which serves to restore the balance of the upper part of the trunk. It 

 has likewise been shown by the brothers Weber, to whom we are in- 

 debted for most of our knowledge on this subject, that the forward 

 movement of the lower limbs, though guided by the muscles, especially 

 in the maintenance of such a length of the limb and elevation of the 

 toes, as will prevent these from striking the ground, is, mechanically 

 considered, and in the main, a pendulum motion ; and that the weight 

 of the limb itself is, in part, supported, as already explained, by the 

 pressure of the atmosphere transmitted to the hip-joint. The full 

 swinging movement of the lower limb, allowance being made for the 

 forward motion, through space, of the acetabulum, or point of suspen- 

 sion, is almost exactly equal to the oscillation of a pendulum of the 

 same length, at the same part of the earth's surface, both in extent 

 and velocity. The economy of muscular power thus obtained, is suf- 

 ficiently obvious. 



In leaping from both feet, the muscular acts, unlike those performed 

 in walking and running, are symmetrical on the two sides of the body. 

 The centre of gravity is first lowered considerably, by the bending of 

 the joints of the lower limbs, and by leaning forwards with the trunk ; 

 in this position, a line let fall from the centre of gravity, passes down 

 through the balls of the toes, from a point anterior to the sacro-lum- 

 bar articulation, in consequence of the forward projection of the head 

 and arms. By the sudden and violent contraction of the extensor 

 muscles of the lower limb, which are much stronger than the flexors, 

 that is, by the powerful action of the muscles of the calf, of those in 

 front of the thigh, and of the gluteal and other muscles at the back of 

 the hip, the more or less acute angles formed at the ankle, knee, and 

 hip, are simultaneously opened, and the centre of gravity is lifted up- 

 wards, or upwards and forwards, according to the inclination of the 

 trunk, or to the special direction of the impulse. Leaping consists, 

 therefore, of a series of jerks of the body, produced by single power- 

 ful efforts. In leaping, the legs are first drawn after the body, but 

 they soon advance forward to receive the descending weight ; and 

 leaping is distinguished from running, in this : that the centre of 

 gravity is raised so high, and for so long, in the air, that the lower 

 limbs are able to complete their forward oscillation, and so accomplish 

 a very long step or leap. In the combination of leaping with run- 

 ning, the velocity of the body acquired in the former act, is super- 

 added to the impulse of the leap, and so the total length of the spring 

 is increased. The forward impulse of the body is shown by the move- 

 ment of the arms in alighting. Hopping is performed on similar 

 principles to the leap, but the spring takes place from one leg only. 



There are some other movements which need not be particularly 

 described, such as creeping, and climbing, or letting one's self down a 

 rope or tree. Swimming is a special, mode of progression, which will 

 be presently noticed. 



Locomotion of Animals on Solids. 



In the higher Quadrumana, generally, the attitude of the body, in ordinary 

 progression, is semi-erect, and in the very highest, especially in the gorilla, if 





