Having lifted up the arm in the act of climbing, and having grasped something, the third motion commences, the object being to draw up the body to the wrist and fingers, which of course remain as fixed points. All the muscles which intervene between the fore-arm bones and the spines of the back have to contract and shorten, so as to bring the last-named bones towards the fixed point, and they may be divided into three groups—those which reach from the arm-bones to the blade-bone, those which connect the blade-bone and the back-bone, and those which unite the arm and the back-bone. All contract at once and shorten the distance between the body and the arm; some fix as it were the blade-bone, and twist it slightly, placing it in a straight line for the pulling of others; and the most important bend and pull down the elbow. Two muscles may be noticed in particular. One which has already been noticed forms the lump on the front of the arm when the wrist is brought close to the shoulder, and is called “biceps,” because it has two heads or points of adhesion to the blade-bone, not far from the joint of the arm-bone. The fibres pass over the arm from the blade-bone down to one of the bones of the fore-arm, in front of the bend of the elbow, and when they contract they tend to bend the elbow and bring the wrist near the shoulder, or the shoulder near the wrist when the fingers are fixed or clasping. The biceps of the Gorilla is a vast muscle, but it wants the symmetry of that of man, and it does not taper downwards so as to make the arm narrower above the elbow. Another muscle is at the back part of the arm, and from having three upper heads or attachments is called the “triceps.” Two of the heads are attached to the arm-bone, and one to the blade-bone, and the lower one is fixed on to the piece of bone of one of the fore-arm bones, on which the arm rests when “elbows are on the table.” Its action is to drag the blade-bone towards that bone, and it is assisted in this by a muscle which passes from the spine to the arm-bone, and whose office in climbing is to drag the spine towards the arm. Finally, there are numerous muscles which pass from the long spines of the pieces of the back-bone (vertebræ) to the blade-bone, and which in climbing tend to drag the first towards the last-mentioned bones, and to move the body generally upwards. The huge size of the blade-bone assists in this in the Gorilla, as its large surface can give adhesion to larger muscles than a smaller one; and as the arm-bones are large, there is all the more room for muscular play.
Considering the bulk of the body of a Gorilla, and the nature of the movements of climbing, it is to be expected that those muscles and bones which are connected, as just stated, with the blade-bone, should be large and strong. This is remarkably the case. On examining the back of a Gorilla one is struck with the great projection of the back-bones in the neck. In man each back-bone or vertebra has a projection or spine which sticks out backwards more or less. These are small in the region of the neck, but in the Gorilla these spines are very long there, and give a peculiar hump-necked appearance. Their size, however, is in exact relation with the size and strength of the muscles attached to them, and some of these go to the blade-bone to assist in the act of climbing.
It is this hump-necked appearance and the round-backed look produced by the great size of the blade-bones which make a Gorilla so ugly about the chest and head, but beauty is of much less use in an African forest than good stout bones and active muscles.
The hind part of the neck does not form a graceful curve as in a well-made man, but a projection which gradually slopes into the line of the back. Moreover, the shoulders of the Gorilla do not slope from the neck—on the contrary, their direction is that which renders the hand-over-hand movement of climbing the readiest of commencement. They are “high,” as the term is, the head and neck being as it were sunken between them, so that the chin, instead of being on a much higher level than the top of the breast-bone, is naturally lower than it. The front of the neck is thus hidden by the huge lower jaw.
Gorillas have collar-bones which are in the same position as those in man, but they are straighter, stouter, and stronger: they are not placed almost horizontally between the front of the blade-bone and the breast-bone, as in us, but as the shoulders are “high” they slant downwards to the breast-bone. By placing the hand on the upper part of the opposite side of the chest the collar-bone may be felt with the tips of the fingers like a ridge, and it is one which many know to their cost is very readily broken by a fall on the end of the shoulders. The bone is something like the letter f in outline, without the cross-bar, and it is fixed at both ends: so when a force acts on one end in the direction of the length of the bone it tends to bend, and often cracks and breaks across.
Now a fractured collar-bone would be a serious thing to a Gorilla; he could no longer lift up his arm, and he would be in constant peril and difficulty; hence, Nature has given him not only a very strong and straight bone, but has by the “high” shoulder posture rendered a fall on the top of it almost impossible. A fall would probably injure the upper part of the arm, which is well protected by the thick cushion of muscle, flesh, and hairy skin which covers the bone.
Travellers and hunters have noticed the rapidity and ease with which the Gorilla moves when off the ground, and when the size and the weight of the animal are considered it becomes evident that not only must it have great muscular power but a stout heart, good circulation, and capital “wind.”
It must be remembered also that it is a great eater of vegetable food, and that it has to consume a large quantity to obtain a supply of nourishment: in other words, it has a very capacious stomach, which has to be carried about and kept very well filled.
In order to meet these requirements there is a very capacious chest (much more so than in man), which contains the large lungs and heart, and the belly is flaccid and large, so that the stomach need not press upwards and interfere with the breathing, or with the action of the circulation. Man has twelve ribs on either side, but the Gorilla has thirteen, each of which is longer, stouter, and broader than ours, the result being to make the cavity enclosed by them the greater, but apparently less readily influenced by the muscles of respiration.
When we breathe deeply and endeavour to inspire more than is usual we employ certain muscles which act on the ribs, enlarging the cavity of the chest, and then diminishing it as the expiration occurs. The larger the spaces between the ribs, and the more elastic the ribs themselves, the greater is their possible amount of movement. In us it is very great in the child, great in man, but much less in old age, when the elasticity of the ribs diminishes. In the Gorilla, the breadth and strength of the ribs keep the cavity of the chest always vast, and certainly from their solidity and from the small space which exists between the successive ribs, great and unusual efforts of respiration are not very possible. So large is the cavity of the chest in the Gorilla, and so capacious are the lungs, that it is possibly not necessary for it to put itself out of breath, and to call extraordinary muscular exertion into play, during its uneventful life.