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20 involved some anatomical alterations in the structure of the body. Not only were the bones of the limbs adapted to perform their respective functions under the new conditions, but the spine had to be turned by a quarter of a circle, so as to be in the vertical direction, i.e. in line with the posterior limbs. The skull, which was formerly supported by a powerful muscle (Ligamentum nuchæ), moved backwards until it became equipoised on the top of the vertebral column. The upper limbs, now relieved from having any share in the locomotion of the body, assumed great freedom in the various movements of flexion, pronation, and supination. The fingers became longer and could be opposed, singly or in groups, to the thumb so as to form a hook, a clasp or a pair of pincers; and the palm of the hand could be made into a cup-shaped hollow capable of grasping a sphere. In fact, the hand of man is the most perfect piece of mechanism Nature has yet produced. But these morphological changes involved no obliteration of the primary homologies common to the rest of the higher vertebrates. All the bones, muscles, nerves, blood-vessels and sensory organs remained much the same as those of the anthropoid apes, which are the nearest of kin to man. But if the races of mankind are so closely related both in structure and mode of development to the anthropoid apes, what, it may be asked, are the essential characters which differentiate them from the latter? The authors of Mammals