In making its way through the forest, and in climbing so constantly that any position on the ground is rare, the great length of the fore limbs is of immense use to them. They nearly touch the ground, so long are they, when the creature is erect, and this peculiarity separates them from the Chimpanzees. In climbing, the blade-bone is of great importance; and in the Orang it is broader, and more like that of man than in the Chimpanzee and Gorilla, and its spine is inclined upwards; and one of the processes of the blade-bone which has to do with the muscles which pass from the shoulder to the arm, and which is called the coracoid, is more inclined downwards than in the Apes already described. Now, the blade-bone of the Chimpanzee and its coracoid are admirably adapted for climbing; why are they not, therefore, exactly like those of the Orang, and vice versâ? This is not a difference produced by adaptation of means to ends, but one which relates to the origin of the two animals, and to those which preceded them. The same is the case in respect of the wrist of the Orang. It has one bone more than the Chimpanzee, which has the same number as in other Troglodytes, and in man also. This bone is fixed in between the two rows of the bones of the wrist, and is called the “intermediate,” and is found in the Monkeys which are below the Orang in the animal scale. It is an offshoot of the scaphoid bone.
Oddly enough, although the number of the ribs of the Troglodytes is thirteen, and probably in one of them there are fourteen, there are only twelve in the Orang; and the breast-bone, which consists of a large upper bone and several smaller ones (united above and below to each other, in the Troglodytes), has these bones separate and halved, as it were, sideways in the Orang, resembling in it the condition of the bones of the immature man. In the Troglodytes the round top of the thigh-bone, where it fits into its socket, the hip, has a kind of rope-like ligament attaching the one bone to the other, but this does not exist in the Orang. The knee-cap is very small, and the heel-bone hardly projects backwards in the Orang, and the “toe-thumb” sticks out at right angles from the foot, being about one-quarter of its length. The Orang is a great climber, and rarely, if ever, walks on its sole, which the Chimpanzee can do slightly. The general appearance and the nature of the movements of the foot of the Orang is that of a thin “club foot.” All the turning-in of the bones of the foot in the Chimpanzee is exaggerated in the Orang, whose toe-thumbs are capable of great activity. Tame Orangs may be noticed to use the foot, which is longer than the lower leg, in climbing, as perfectly as the hand; and it appears that the frequency of their movements of grasping, rather than of delicate prehension, tends to the last joint of the “toe-thumb” becoming small and losing its nail.
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]
ORANG AND NEST.
Before considering the anatomy of the brain, skull, and the inside of the Orang, it is as well to become aware of some of its peculiarities when young, and in a state of captivity.