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 normal 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 limb. On all such occasions, where the muscular action is brought directly into play in overcoming the weight or resistance, Dr. Buchanan affirms that the right shoulder is much more powerful than the left, but in the passive bearing of weights it is otherwise. The very fact that the centre of gravity lies on the right side gives a mechanical advantage in the use of the left side in sustaining and carrying burdens; and this assigned pre-eminence of the left side and shoulder, as the bearer of burdens, is accordingly illustrated by means of an engraving, representing “a burden borne on the left shoulder as the summit of the mechanical axis passing along the right lower limb.”