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.