106. =Support of the Centre of Gravity in Animals.=--The base of support which quadrupeds have, viz., the space included between their four feet, is quite large; and this is one reason that they walk so soon after birth. A child does well that can walk at the end of ten or twelve months, for the supporting base is quite small compared with that of a quadruped. It consists of the feet and the space between them. It requires skill, therefore, in the child to manage the centre of gravity in standing and walking, and this is gradually acquired. If one should grow up without ever standing on his feet, he would find, as the infant does, that some training is necessary to enable him to do it. It is on account of the smallness of the base furnished by the feet that the statue of a man is always made with a large base or pedestal. Although we exert considerable skill in walking, by no means so much is requisite as the Chinese ladies must put in exercise with their small feet. Still more skill is exercised by one who has two wooden legs, or one who walks on stilts. The base made by the feet can be varied much by their position. If the toes be turned out and the heels brought near to each other, the base will not be as large as when the feet are straight forward and far apart, as is manifest in Figs. 56 and 57. It is for this reason that the child, in his first essays at standing and walking, instinctively manages his feet as in Fig. 56. [Illustration: Fig. 58.] [Illustration: Fig. 59.] [Illustration: Fig. 60. Fig. 61.] 107. =Motions of the Centre of Gravity in Walking.=--In walking, the centre of gravity is alternately brought over one foot and the other, and so moves in a waving line. This is very manifest as you see people before you going down the aisle out of a church. When two are walking together, if they keep step the two waving lines of their centres of gravity run parallel, as in Fig. 58, and they walk easily; but if they do not keep step these lines run as in Fig. 59, and the movement is both awkward and embarrassing. The line of movement of the centre of gravity is always slightly waving _upward_ also, as seen in Fig. 60 (p. 78). In the case of a man with wooden legs the line would not be gently waving, but somewhat angular, as represented in Fig. 61. [Illustration: Fig. 62. Fig. 63.] [Illustration: Fig. 64.] [Illustration: Fig. 65.]