To the most superficial observer it is manifest that the anatomical disposition of the vital organs is not symmetrical. The heart lies obliquely, from above downwards, and from right to left; the trachea is on the right side, and the right and left subclavian veins and arteries are diversely arranged. There are also three lobes of the right lung, and only two of the left; and the liver is on the right side. Here, therefore, are sources of difference between the right and left sides of the body, which, if subject to variation, offer a possible explanation of the phenomenon that has so long baffled physiologists. To the variations in the disposition of those organs attention has accordingly been repeatedly directed; as in the occasional origin of the left subclavian artery before the right, which, as hereafter noted, Professor Hyrtl suggested as the cause of the transfer of dexterity to the left limb. But instances have repeatedly occurred of the entire transposition of the viscera. “There are men born,” says Dr. Buchanan, “who may grow up and enjoy perfect health, in whom the position of all the thoracic and abdominal viscera is reversed. There are three lobes of the left lung and only two of the right; the liver is on the left side, and the heart is on the right; and so forth.” Those and other malformations, as well as pathological lesions, especially if they occur in early life, may affect the relative power of the two sides; and Dr. Buchanan at a later date reported a case that came under his own notice, in which the entire transposition of the viscera coexisted with left-handedness. But he had already adopted the mechanical theory, subsequently modified, as explained above; and it is only in a closing remark in his paper of 1862 that he makes a passing reference to this remarkable coincidence.