From the Introduction. Helvetius, in 1758, in an essay on "The Mind," quoted by H. T. Buckle in his "Introduction to the History of Civilization," maintains as an incontrovertible fact that the difference between man and animal is a result of the difference in their external form; that if for example the wrists instead of ending in hands with flexible fingers had ended like a horse's hoof, man would have remained a wanderer on the face of the earth among the animals, ignorant of every art and entirely defenseless; that this structure-the hand-is the sole cause of our superiority. Ever since the genesis of the human race, the hand has been the indispensible instrument of its continued advance. About the creations of this hand, in science and in art, an endless succession of volumes has been written; to the hand, also, many scientific works are devoted; but the writer has not discovered a single volume devoted exclusively to the depicting of the hand. It is the purpose of this work to present the hand not only to the eye, but to the understanding.