HAND AND LEFT-HANDEDNESS. 27 
ment, 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 foetal 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. But the premises of Gratiolet are disputed ; and even if proved, they must raise 
further questions, not merely as to the origin, but also as to the influence of such an 
unequal development of the brain on the action of the limbs. 
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 prima- 
rily 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. 
This theory is based, not merely on the preponderance of the liver and lungs on the 
right side, but on these further facts: that the right lung is more capacious than the left, 
having three lobes, while the left has only two; that the liver, the heaviest organ of the 
body, is on the same side ; and that the common centre of gravity of the body shifts, more or 
less, towards the right, according to the greater or less inspiration of the lungs, and the 
consequent inclination of the liver resulting from the greater expansion of the right side 
of the chest. Herein may possibly lie one predisposing cause leading to a preferential 
use of the right side. But the evidence adduced fails to account for what, on such a 
theory, become abnormal deviations from the natural action of the body. The position 
of the liver, and the influence of a full inspiration, combine, according to Dr. Buchanan, 
to bring the centre of gravity of the body nearly over the right foot. Hence in actively 
overcoming a resistance from above, as when the carter bears up the shaft of his cart on 
his shoulder, the muscular action originates mainly with the lower limb of the same side, 
which partakes of the same muscular power and development as the corresponding upper 
