It is an axiom, generally recognized in neurophysiology, that the development of skilled acts in the upper and lower extremities of the highest forms of animal life is intimately connected with the size of the pyramidal tracts. The work of Schaefer1 is quoted as giving experimental evidence of this thesis, and Tilney2 concluded from comparative studies of the central nervous system of apes and man that "it is in relation to the progressive adaptation apparent in the upper extremities that the pyramidal system is most intimately connected.... It seems permissible to conclude that the increment in pyramidal volume is proportional to that increasing demand for control of motor performances made possible through the progressive development of the hand."
In studying the literature on this subject one finds that comparative measurements of the pyramids in the medulla oblongata and the size of the nonmedullated tract in new-born animals form
WEIL A, LASSEK A. THE QUANTITATIVE DISTRIBUTION OF THE PYRAMIDAL TRACT IN MAN. Arch NeurPsych. 1929;22(3):495–510. doi:10.1001/archneurpsyc.1929.02220030072007
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