168 SPECIAL PHYSIOLOGY. 



pelvis upwards upon the ribs ; and lastly, the head is supported for- 

 wards upon the trunk, chiefly by the action of the sterno-niastoid 

 muscles. 



In the sitting posture, as upon a chair (and also in that upon the 

 ground), the weight of the trunk is supported upon the tuberosities of 

 the ischia, and not upon the lower end of the vertebral column or 

 coccyx: but, in this attitude, the weight is partly balanced, and sup- 

 ported by the thighs resting upon the chair, whilst the feet, touching 

 the ground, serve to steady the thighs. 



In rising from such a posture to the erect attitude, the relative posi- 

 tions of the base of support, and of the centre of gravity, are instinc- 

 tively adjusted, so as to economize, as much, as possible, the muscular 

 force. The body has, in fact, now to be supported upon the compara- 

 tively narrow base of the two feet ; whilst its centre of gravity has to 

 be elevated in the air, by the additional length of the thigh bones. 

 Accordingly, when we rise from a chair, we draw backwards one or 

 both feet close to, or even beneath the chair, and then incline the body 

 forwards, so as to bring its weight as much as possible over the future 

 base of support; when, by the contraction of the muscles of the calf, 

 acting from below, the leg bones are brought into a vertical position 

 over the ankle-joints; by the muscles in front of the thighs, acting 

 from the patellae, the thighs are drawn into a vertical position upon 

 the legs ; by the muscles at the back of the thighs, and by the great 

 glutei and other muscles at the back of the pelvis, this latter part of 

 the skeleton, together with the trunk generally, is rolled backwards, 

 and so erected upon the heads of the thigh bones ; by the muscles of 

 the back, the vertebral column is drawn into the upright posture; and 

 lastly, by the muscles at the back of the neck, the head is supported 

 upon the vertebral column, with the face directed forwards. In this 

 action, then, of rising from the sitting posture, the several angles be- 

 tween the foot and leg, the leg and thigh, and the thigh and trunk, are 

 opened out ; and the body assumes its extreme length. 



The erect posture, the characteristic attitude of man, is therefore 

 by no means a passive, but, essentially, an active attitude; and, though 

 not locomotive, in reference to the base of support, is really a loco- 

 motive act in reference to vertical space above the base of support. 

 It requires, indeed, the active and energetic employment of a multi- 

 tude of muscles, not only to assume it, but also to maintain it, as is 

 well illustrated by the facts, that children are unable to stand until 

 after many trials, and that adults stumble, or fall, when the nervous 

 power, which commands or controls the muscles, is lessened or sus- 

 pended, as in drunkenness, apoplectic seizures, fainting, or sudden suf- 

 focation ; in which cases, the body, with its system of internal movable 

 levers, the bones, doubles at its various angles, collapses, and falls to 

 the ground. Nevertheless, we find on examination, that these bones 

 are admirably constructed, and shaped for supporting their own weight, 

 and the weight of the parts attached to them, in the erect position, 

 every portion of the skeleton, affording directly, or indirectly, evi- 

 dences of design in its adaptation to that posture (see Figs. 1, 2). 



Thus the human foot, from its great breadth, the flatness of the 



