More recently, Dr. Humphry of Cambridge has discussed the cause of the preferential use of the right hand in his monograph on _The Human Foot and Human Hand_, but with no very definite results. Many attempts, he says, have been made to answer the question, Why is man usually right-handed? “but it has never been done quite satisfactorily; and I do not think that a clear and distinct explanation of the fact can be given. There is no anatomical reason for it with which we are acquainted. The only peculiarity that we can discern is a slight difference in the disposition, within the chest, between the blood-vessels which supply the right and left arms. This, however, is quite insufficient to account for the disparity between the two limbs. Moreover, the same disposition is observed in left-handed persons and in some of the lower animals; and in none of the latter is there that difference between the two limbs which is so general among men.” Dr. Humphry accordingly inclines to the view that the superiority of the right hand is not natural, but acquired. “All men,” he says, “are not right-handed; some are left-handed; some are ambidextrous; and in all persons, I believe, the left hand may be trained to as great expertness and strength as the right. It is so in those who have been deprived of their right hand in early life; and most persons can do certain things with the left hand better than with the right.” So far, therefore, Dr. Humphry’s decision would appear to be wholly in favour of the conclusion that the superiority of the right hand is an acquired habit. But after stating thus much, he adds: “Though I think the superiority of the right hand is acquired, and is a result of its more frequent use, the tendency to use it in preference to the left is so universal that it would seem to be natural. I am driven, therefore, to the rather nice distinction that, though the superiority is acquired, the tendency to acquire the superiority is natural.”