Landreth, C. (1958). Motor behavior. In C. Landreth, Knopf publications in psychology. The psychology of early childhood (pp. 75-125). New York, NY, US: Alfred A. Knopf.
http://dx.doi.org/10.1037/13176-004
The motor behavior of the young child has its beginnings in the early weeks of prenatal life, a fact we are artfully reminded of by the title of a recent report, "Fetal Frolics." It has been said that the creative artist tests life in his pulses; it might equally be said that the young child tests life in his muscles. He progressively extends his mental horizon by his ability to focus his eyes and hold his head up, then to sit steadily and survey his world, and finally to move on all-fours or afoot to bring what he sees within reach of his exploring hands, lips, and tongue. The young child assimilates experience and captures impressions in his movements; he is the plane that flies overhead, zooming tip-toe with outstretched arms; he is the racehorse, throwing back his head and arching his back. His activity is the wellspring of his laughter and the most frequent expression of his anger and frustration. It reflects his judgment and mirrors much of his learning. It serves as a rough and ready means of communication until language takes its place. How does this behavior develop? The most striking developmental changes in motor behavior occur within the first two years of life. During this period the child acquires such basic human behavior as an erect posture, upright walking, and manual dexterity in reaching, grasping, and fine manipulation. One has only to contrast these accomplishments in a two-year-old with the helplessness of the newborn to realize how important such behavior is in the development of the individual and the human species. (PsycINFO Database Record (c) 2016 APA, all rights reserved)