The upper arm reaches down from the shoulder to the hips in the Gorilla, and its bone (os humerus, from the Latin) is strongly marked on its surface by roughnesses and ridges, to which the great muscles are attached. In man the shape of the upper arm varies with the strength of the individual, but in the strongest man and in the most beautifully-shaped woman it has a swelling on the front, and tapers more or less towards the elbow. This is caused by the two-headed or biceps muscle, and by other muscles ending in tendons. But the Gorilla has a very shapeless upper arm; it is, as it were, fat and round throughout, and very large above the elbow, and this is because of the size of the bone within, and on account of the muscles not tapering as they do in man, but being well developed right down to their ends. Hence, elegance of shape is sacrificed to extra muscular strength and size of bone.
On looking at the arm-bone, which, being connected to the shoulder by a joint, has much to do with the act of climbing and striking, it will be noticed that it greatly resembles that of man in shape, but is longer, stouter, and clumsier. The joint is nearly in the shape of a rounded knob, and the corresponding depression or cup on the blade or shoulder-bone into which it fits, is an oval and concave surface, and they are kept close together by a kind of capsule which stretches from one bone to the other and encloses the joint. Perfect freedom of movement is insured by the bones being covered with glistening cartilages, and a delicate and moist membrane, and the motion from the shape of the apparatus is almost equal to that of a chandelier where there is what is called a cup-and-ball joint at the ceiling. It has already been noticed that muscles are attached to the blade-bone and to the arm-bone below the joint, and that, this being movable, when they contract they move the arm, and the instance was given of the action of the deltoid muscle in raising the arm. In the Gorilla, this great muscle reaches lower down than in man, and there is a very strong mark in the shaft of the bone for its insertion. This gives the muscle greater play than in us, and enables it to lift, more slowly perhaps, but more efficiently, for the arm-bone between the joint and the place where the muscle is attached, is the long arm of a lever which is shorter in man. Below the globular head of the arm-bone is the shaft or cylindrical part of the bone which gives origin to the three-headed muscle called triceps, and is covered by the two-headed one (biceps) already mentioned, besides the deltoid. A deep groove allows one of the ends or heads of the biceps to pass along and slide over the joint and to reach the shoulder-blade. The shaft as a whole is more or less cylindrical, with a slight angular outline, the angles being projections of bone which strengthen the whole, besides giving attachment to muscles; the cylindrical shape is the best for strength and lightness, and these properties are increased by the adoption of a plan which engineers have long since unwittingly copied. The shaft is hollow, and is cellular at both ends, solid bone covering the outside, conditions which oppose fracture, and produce increased strength, indeed greater strength and lightness than a solid bone would have. Below the shaft is an expansion, on which are placed the surfaces for the jointing on of the two bones of the fore-arm, and the bone is especially in old Gorillas perforated there, a condition seen in some very old human bones. There is an important point in the relative length of the upper arm-bone, and the bones of the fore-arm in the Gorilla, in other Apes, and in man, for in this great Ape and in us the humerus is longer than the others, and in the Chimpanzee they are almost equal, whilst in the rest of the Monkeys they are very unequal, the bones of the fore-arm being much the longest.
Although they have such strong arms, covered with a stout skin and with hairs sloping downwards, the Gorillas sometimes manage to break them, and then Nature endeavours to repair the injury. In the skeleton of the old male Gorilla in the British Museum there are proofs of a former fracture of the humerus or upper arm-bone. The arm was broken across, and as it could not be kept quiet, Dame Nature has not done her work as well as a modern surgeon could on a patient whose arm he could put in splints, for it is thickened, shortened, and twisted.
The fore-arm of the Gorilla has its long hairs pointing upwards to the elbow, and the limb does not slope gracefully towards, and become slightly smaller above the wrist, as in man, but remains thick and fleshy as far as the hand. There are two bones in the forearm which are jointed above with the lower end of the arm-bone (humerus), and which are also connected by joints at their lower ends with the small bones forming part of the wrist. The bones of the fore-arm are called the radius and the ulna in the Gorilla as in man. They are larger, stouter, and wider apart in the great Ape than in ordinary Europeans, but they greatly resemble those of the Australian aborigines. As these bones are covered with muscles, some going to the fingers, and others coming from the upper arm, there are many ridges or surfaces on them, for their origin and attachment, and these greatly resemble those of man; moreover, the muscles perform the same functions and movements.
When compared with that of a strong man, the wrist of the Gorilla is broader, and the bones, of the same number, are larger from side to side, and this extra breadth makes this part of the hand very wide. As the Gorilla’s hand often has to support the weight of the body, on the back of the fingers and knuckles, it is long, broad, and very strong, surpassing in these respects those of man; but the thumb is peculiar. It does not look a well-formed one; it is evidently short, and out of proportion to the long fingers. The human thumb reaches not far from the second joint of the fore-finger; but the top of that of the Gorilla is on a level with the first joint, or at the end of the long bones of the hand, and which are called metacarpal bones.
Remarkable then for its breadth and thickness, the Gorilla’s hand has also a long palm, which is not only due to the length of the bones, just mentioned, but also to the fact that the web or undivided skin between the fingers, where they join the hand, is not slight as in man, but long and very decidedly visible. The web extends half way up the first joint of the fingers. The fingers are therefore made to appear short[7] (although their bones are long), and they look dumpy and swollen, and this appearance is increased by there being callous pads of skin on the back of the middle and end joints. Finally, the fingers slope to the nails, which are not much larger or longer than those of man. The back of the hand is hairy as far as the divisions of the fingers; and the callous pads, just noticed, almost do away with the appearance of some of the joints. The short thumb, not so big as the forefinger, has a nail which does not reach the end of it, and the under-parts of the thumb, fingers, and palm have a bare skin. Professor Owen, in summing up the difference between the structure of the hands of the Gorilla and of man, remarks that in the great Ape the hands are instruments for great power of grasp, and for sustaining great weight, and the length and strength of the whole upper limb accord with their mechanical powers and requirements. In man, the framework of the hand bespeaks an organ of varied and delicate prehension, and the form and proportion of the rest of the arm-limb relate to the free motions and complex functions of the instrument.
Having raised the arm by its muscles, the fingers and thumbs grasp an object, or, in other words, certain muscles which are placed between the bones of the fingers and between the fingers and the bones of the fore-arm, contract and move the bones, which are jointed. The tops of the fingers are bent on the palm, and the thumb is closed on them, and this continues as long as the contraction permits. All the apparatus for long-continued clasping is present in the Gorilla, and there are nearly the same kinds of muscles employed as in man. There are, however, some differences, to one of which it is necessary now to allude. The thumb, for instance, of the Gorilla is of great importance in grasping, but it has not to perform such complicated movements in other things as that of man. In man its movements are most wonderful, and by using one muscle after the other which belongs to it, it can be moved so as to describe a circle with its tip. This is done in the action of “twiddling,” but also in many others where the will hardly influences the muscle, and where the thumb may be said to be moved unconsciously. Gorillas in their quietest and most reflective moods cannot indulge in the sober practice of twiddling, for an important twiddling muscle is absent in them. But it is no great loss, and perhaps it is a real gain, for this muscle would be in the way of rapid clasping, as it rather tends to keep the thumb from the fingers. Whilst the great Ape is thus deficient it has a muscle on the other side of the hand which is not possessed by man, and whose office appears to be to separate as far as is possible the fourth and fifth fingers (their first joints), and by so doing to enlarge the grasp of the whole hand. As the hand of the Gorilla is at least a third larger than that of the averaged-sized man, there is of course a corresponding increase in the space which can be grasped. The muscles are stronger and stouter than in us, and therefore the hand is a more powerful one. Nevertheless it is incompetent of performing many actions which are readily done by a child.
HAND BONES OF THE GORILLA.