There are some interesting points about the relation of the construction of this animal and its method of moving. Thus, in grasping a bough with the arm at full length above the head, so as to leave it with a swing in order to grasp another rapidly and for a correspondingly short period of time, the fingers require to be kept together as much as is possible, and to remain more or less bent on the palm. The long thumb may or may not be used, but in order to move efficiently it must be free, and also strong. Now in the Siamang these necessary peculiarities are present, and the common use of the finger and thumb in taking hold of things in the ordinary manner is sacrificed to them, and there is little or no delicacy of fingering or of prehension. Moreover, the fingers and thumbs are extremely thin and delicate, and in order to render the first finger less movable, it is, to a certain extent, deficient in its muscles of extension; and the common bending or flexor muscle of the fingers is very independent of that of the thumb. In compensation there is a special muscle found in this genus alone, which pulls the top of the second finger towards the thumb.[20] The skeleton of the hand shows that the fingers are slightly curved. There is no doubt that the hand of the Siamang, although it has these peculiar muscles, the curve of the bones, and also the extra bone noticed in the Orangs, is, as far as its skeleton is concerned, much more human than that of the other Apes. The extensor muscles of the fingers resemble those of the Orangs. The hand is larger than the foot in these animals, and the forearm is much longer than the upper arm. A French naturalist states that the animal can leap, or, rather, swing--for it is done with the fore limbs--with graceful agility at least eighty feet, and the muscles of the arm, which are connected with the chest, aid in this. The pull is from the stationary arm to the chest of the movable body by muscular contraction; and the greater the muscular connection between the arm and chest, the greater will be the movement. In order to provide for this, the great muscle of the front of the upper arm, the biceps (see page 26), is not only attached, as in the other Apes and in man, to the blade-bone just above the arm-joint, but also to the chest in front, for it is united there with the great muscle which springs from the ribs and breast-bone, and is attached high up to the arm (_pectoralis major_). In some of the other Apes this second part of the biceps is attached to a bent projection (coracoid) of the blade-bone, so that it has no direct attachment with the chest itself.