With the attention that is now definitely given to this assignment of the preferential use of one or the other hand to greater or less development of the opposite cerebral hemisphere, renewed observation has been directed to the cerebral source of predominant right-handedness. The discussions in the columns of _Science_, suggested by Professor Baldwin’s study of its first manifestations, have revived the reference of it to the assumed excess in development of the left cerebral hemisphere. Dr. T. O’Connor of New York thus reasserts it as an unquestionable though little-known fact: “But it may not be generally known that the left cerebral hemisphere is larger than the right, its inner face (at the great longitudinal fissure) coming very near to the middle line, while the corresponding inner edge of the right hemisphere is well to the right of the median line. The existence, then, of greater nutrition and greater functionating ability in the left hemisphere might well be assumed. But that there is a reason for the greater size, development, etc., of the left hemisphere is evidenced by a study of the conditions of blood-supply to the two hemispheres. The left carotid artery ascends almost perpendicularly, so as to form, as it were, an elongation of the ascending aorta, while the right carotid is given off from the _arteria innominata_. The right vertebral artery is given off by the subclavian after the latter has described its arch and become horizontal, but the left vertebral arises from the apex of the subclavian’s curve. There is thus the distinct advantage to the left hemisphere of a better blood-supply because of the much straighter course taken by the great channels carrying it” (_Science_, 12th December 1890).