[13] They have several muscular peculiarities. Thus the great muscle of the hind part of the loins (sacro lumbalis) is vast and fleshy in man, but it is reduced to very small proportions in the great Apes. The great oblique muscle of the body is not attached to the hip, and the muscles of the buttocks are reduced excessively in the Apes. All this renders their erect position difficult and not usual. The motions of the shoulder and arms are assisted by extra muscles; one stretches from the sixth neck-vertebra to the first rib, another reaches from the outer part of the collar-bone to the neck in front, to the bone under the tongue (hyoid bone), and a third from the collar-bone to the side of the first vertebra. The small muscle of the chest (pectoralis minor) reaches to the capsule which surrounds the shoulder-joint. There is an extra muscle, which reaches from the back to the elbow, and which allows the animals, when hanging by one hand, to turn and twist the body slightly. The metacarpal bone of the little finger has a special muscle, which tends to enlarge the grasp of the hand. The great Apes have, however, an imperfect or deficient proper flexor to the thumb, and the extensor of the first joint of the thumb is wanting. The ill-developed “calf” has not its two great muscles combined in the one tendo Achillis, as in man, and the muscles of the foot are so arranged that they permit of much more independent motion than those of man have.
[14] Simia satyrus. Simia morio.
[15] The Transversus pedis.
[16] A muscle, called the accessory flexor of the toes, is absent in the Orangs, and one termed scansorius, or climber, exists on the outside of the hip and the joint of the thigh.
[17] * Is the intermediate bone.
[18] Hylobates.
[19] Hylobates syndactylus.
[20] The abductor of the third joint of the second finger. The thumb counts as the first finger.
[21] Hylobates lar.
[22] Hylobates hoolook.