A huge air-pouch is packed away in front of the windpipe and amongst the muscles of the neck, as in the Apes already noticed, and it commences in the so-called ventricles of the larynx. Its extension amongst the upper muscles of the chest is most remarkable, for when full of air, these being relaxed, it must blow out the upper part of the body and neck in a singular manner. One of the muscles of the chest, common to man and Apes, the great pectoral (_pectoralis major_)--which has already been noticed as springing from the ribs, the breast and collar-bone, and to be attached in front of the groove in the upper arm-bone--is not a continuous sheet of muscular fibre as in man, but is divided into a number of bundles, there being at least three great ones. Now, it is between these and in their intervals that the vast laryngeal air-pouch is found on the chest. Great as it is, however, it does not appear to have anything to do with the voice, except, perhaps, to produce resonance during distension. The muscles of the hips, thigh, and leg-bones of the Orang cannot be distinguished generally from those of the Chimpanzee; but it is evident that the position of some is such as to make straightening of the knee very difficult, and on the contrary, they assist jumping and climbing, or any movement in which it can be kept permanently bent. As it is most convenient for the foot of the Orang to be well expanded during climbing or holding on, and not for its bones to be too much forced together sideways, the animal is deficient in a muscle which exists in man,[15] and which stretches transversely across, between the ends of the metatarsal bones. In like manner the inability of the thumb to perform many separate actions is produced by the absence of the flexor muscle; but there is a slip of a muscle whose tendon reaches the first joint, and its office is to oppose the thumb, not to the palm of the hand, but to the first joint of the second finger. This is a monkeyish peculiarity. The animal, using as it does its short toe-thumb for grasping forcibly, requires all the power possible to be exercised between its bones and those of the ankle. Hence it has a muscle which exists in the hand but not in the foot of man, and which, from its drawing the bones together, is called the _opponens_ (of the great toe). This does not appear to exist in the Troglodytes. The other most important peculiarities of the muscles which relate to the greater but less independent movement of the toes and fingers, are the connection of the long flexor of the “toe-thumb” with the lower and outer part of the thigh-bone, and the possession of a complete set of deep extensor muscles for the four outer fingers. The extensor of the first, and the corresponding muscle of the little finger, subdivide to supply the third and fourth. This is the case in the next group of Apes also, but in the Troglodytes each of these muscles has but a single tendon.[16] [Illustration: ORANG AND NEST.]