Physically considered, the chimpanzee very closely resembles man, but there are certain points in which he differs both from man and from other apes. We may notice a few of these points. The model of the ear of the chimpanzee closely resembles that of man, but the organ is larger in size and thinner in proportion. It is very sensitive to sound, but dull to touch. The surface is not well provided with nerves. He cannot erect his ear, as most animals do, by the use of the muscles at the base; but, like the human ear, the muscles are useless, and in this respect the ear is fixed and helpless. The hand of the chimpanzee is long and narrow. The finger bones are larger, in proportion to their size, than those of the human hand. One thing peculiar to the hand of the chimpanzee is that the tendons inside of the hand (those called the flexors), which are designed to close the finders, are shorter than the line of the bones. On this account the fingers of the ape are always held in a curve. He cannot straighten them. This is probably due to the habit of climbing, in which he indulges to such a great extent. He also indulges in the practice of hanging suspended by the hands. In making his way through the bush he often swings himself by the arms from bough to bough. Sometimes he suspends himself by one arm, while he uses the other to pluck and eat fruit. This characteristic is transmitted to the young, and is found in the first stages of infancy. The thumb is not truly opposable, but is inclined to close towards the palm of the hand. It is of little use to him. His nails are thick, dark in color, and not quite so flat as those of man. The great toe, instead of being in line with the others, projects at an angle from the side of the foot, something after the manner of the human thumb. The foot itself is quite flexible and has great prehensile power. In climbing, and in many other ways, it is used as a hand. The tendons in the sole of the foot are equal in length to the line of the bones, and the digits of the foot can be straightened; but from the habitual use of them in climbing, the ape is predisposed to close the digits, wherefore the foot is naturally inclined to curve into an arch, especially in the line of the first and second digits.