This idea of a greater development of the left cerebral hemisphere has been the subject of considerable diversity of opinion. A marked difference in the weight of the two hemispheres has indeed been repeatedly asserted by well-qualified observers as the result of careful investigation. M. Broca stated that in forty brains he found the left frontal lobe heavier than the right; and Dr. Boyd, when describing the results obtained by him from observations on upwards of 500 brains of patients in the St. Marylebone Hospital, says: “It is a singular fact, confirmed by the examination of nearly 200 cases at St. Marylebone, in which the hemispheres were weighed separately, that almost invariably the weight of the left exceeded that of the right by at least the eighth of an ounce.” Dr. Brown-Sequard also, as hereafter noted, makes this apparent excess in weight of the left hemisphere of the brain the basis of very comprehensive deductions. Again Dr. Bastian affirms, as a result of careful observation, that the specific gravity of the gray matter from the fronted, parietal, and occipital convolutions respectively is often slightly higher on the left than it is on the right hemisphere. The opinion is thus sustained by some of the most eminent physiologists who have given special attention to the brain and its functions. But, on the other hand, Professor Wagner and Dr. Thurnam both state that their careful independent investigations failed to confirm the results arrived at by M. Broca and Dr. Boyd. From the weighing of the two hemispheres of eighteen distinct brains, Professor Wagner found the right hemisphere the heavier in ten, and the left in six cases, while in the remaining two they were of equal weight. Dr. Thurnam, without entering into details, states that the results of his weighings did not confirm Dr. Boyd’s observations; adding that “fresh careful observations are certainly needed before we can admit the general preponderance of the left hemisphere over the right.” Though the two hemispheres of the brain are sufficiently distinct, they are united at the base; and even with the most careful experimenters, the section through the cerebral peduncles and the corpus callosum is so delicate an operation that a very slight bias of the operator’s hand may affect the results. That a difference, however, is occasionally demonstrable in the weight of the two hemispheres is unquestionable, and the whole tendency of the most recent investigation is to sustain the hypothesis which refers the cause of left-handedness to an exceptional excess of nervous force in the right cerebral hemisphere. But the results to be anticipated from the partial character of the bias in the majority of the right-handed would tend to suggest a doubt as to the full acceptance of the statement of Dr. O’Connor adduced above. It is rather in accordance with what has already been affirmed as to the very partial prevalence of any strongly defined bias in the majority for the preferential