Professor Hyrtl of Vienna, the eminent anatomist already referred to, in discussing the cause of left-handedness in his _Handbuch der Topographischen Anatomie_ (1860), affirms a correspondence between the ratio of left-handed persons and the occurrence of certain deviations from the normal arrangements of the blood-vessels. “It happens,” he says, “in the proportion of about two in a hundred cases, that the left subclavian artery has its origin _before_ the right, and in these cases left-handedness exists, as it also often actually does in the case of complete transposition of the internal organs; and it is found that the proportion of left-handed to right-handed persons is also about two to one hundred.” Professor Hyrtl thinks that ordinarily the blood is sent into the right subclavian under a greater pressure than into the left, on account of the relative position of these vessels; that in consequence of the greater supply of blood, the muscles are better nourished and stronger; and that therefore the right extremity is more used. In cases of anomalous origin of the left subclavian, etc., the reverse occurs, and therefore the left hand is employed in preference. The theory of Professor Hyrtl has this feature to recommend it, that it assigns a cause for the prevalent habit, which, if confirmed, would equally account for the exceptional left-handedness; and no proffered solution of the question, founded on organic structure, is deserving of attention which fails to do so. But the statistics of such internal organic structure are not, like those of the transposition of the heart and immediately related organs, accessible in the living subject, unless in very rare exceptions; and the occurrence of one or two cases in which the deviation from the normal arrangement of the artery, or the entire transposition of the viscera, is found to coexist with left-handedness, may only be misleading.