The eminent anatomist, Professor Gratiolet, turned from the organs in immediate contact with the arm and hand, and sought for the source of right-handedness in another and truer direction, though he failed to realise its full bearings. According to the Professor, in the early stages of fœtal development the anterior and middle lobes of the brain on the left side are in a more advanced condition than those on the right side, the balance being maintained by an opposite condition of the posterior lobes. Hence, in consequence of the well-known decussation of the nerve roots, the right side of the body,--so far as it is influenced by brain-force,--will, in early fœtal life, be better supplied with nervous force than the left side; and thereby movements of the right arm would precede and be more perfect than those of the left. The bearings of this line of argument in its full compass will come more fitly under review at a later stage. Dr. Andrew Buchanan, Professor of Physiology in the University of Glasgow, in a paper communicated by him to the Philosophical Society of Glasgow in 1862, entitled “Mechanical Theory of the predominance of the right hand over the left; or more generally, of the limbs of the right side over those of the left side of the body,” aimed at a solution of the question in a new way. According to him, “the preferential use of the right hand is not a congenital but an acquired attribute of man. It does not exist in the earliest periods of life.” Nevertheless, “no training could ever render the left hand of ordinary men equal in strength to the right;” for “it depends upon mechanical laws arising out of the structure of the human body.” This theory is thus explained: In infancy and early childhood there is no difference in power between the two sides of the body; but so soon as the child becomes capable of bringing the whole muscular force of the body into play, “he becomes conscious of the superior power of his right side, a power not primarily due to any superior force or development of the muscles of that side, but to a purely mechanical cause. He cannot put forth the full strength of his body without first making a deep inspiration; and by making a deep inspiration, and maintaining afterwards the chest in an expanded state, which is essential to the continuance of his muscular effort, he so alters the mechanical relations of the two sides of his body that the muscles of his right side act with a superior efficacy; and, to render the inequality still greater, the muscles of the left side act with a mechanical disadvantage.” Hence the preference for the right side whenever unusual muscular power is required; and with the greater exercise of the muscles of the right side their consequent development follows, until the full predominance of the right side is the result.