The human foot and the human hand

by George Murray Humphry

I have said that the upper limbs resemble the lower in their general construction. There are, however, some important differences; and one of the chief of these is the greater variety and freedom of the movements in the upper limbs. Strength, for the purpose of carrying the body, is the object in the lower limbs. Mobility is the requisite in the upper limbs. Of this one example has already been given in the instance of the thumb as compared with the great toe.

Movements at the Shoulder.

An equally striking example is afforded by the shoulder. In the first place, the “Shoulder-blade” itself can be moved in several directions—upwards, downwards, backwards and forwards;—whereas the “Pelvis,” i. e. the part which bears to the lower limb the same relation that the shoulder-blade does to the upper-limb, is immoveably fixed.

Secondly, the “Shoulder-joint” is so made as to permit a great variety and extensive range of movements to take place. We can move the arm forwards or backwards, as in throwing a ball, or, in sword exercise; we can raise it so that the limb points straight upwards; and we can swing it round in any direction. It is owing to the free movement in this joint that we are able to apply the hand to every part of the body, so as to remove sources of irritation. It is interesting to observe how other animals get on without hands, though they are much exposed to what we should consider great annoyance, as from flies, &c. The Cow, for instance, lashes its hide with its tail. The Cat licks itself with its tongue. The Sparrow dusts itself by the road-side. The Pig and the Donkey roll in the mud. And many of them, as the Horse and the Ox, have a thin muscle, called “panniculus carnosus,” spread out under the skin, which effects those sudden twitchings of the skin whereby they are enabled to jerk off anything that troubles them. In Man the hand answers better than all these methods combined; and it is necessary that it should do so, because his skin is more sensitive and less protected by natural covering than that of any other animal.

Fig. [55].
Chest and shoulders of man.

For this freedom of movement of the arms, so important to the usefulness of the hand, we are much indebted to the “Collar-bones.” These bones, so called because they are placed at the lower part of the collum or neck, extend, horizontally, from the upper edge of the breast-bone, to the processes of the blade-bones which overhang the shoulder-joint. Thus they hold the shoulders apart, and give width to the upper part of the chest. They also steady the shoulder-blades, and afford a point d’appui to the muscles which effect the lateral movements of the arms,—for instance, to the muscles which tend to draw the arms together, as when we hold anything, between the hands, in front of us; and to those which separate the arms from one another, as when we stretch them out at right angles with the body.

Fig. [56].
Chest and shoulders of bird.

Many animals—the Elephant, the Rhinoceros, the Horse and the Ox—have no collar-bones; and they are only able to swing their fore limbs to and fro. They cannot execute any lateral movements. They cannot throw the limbs out sideways, nor press their fore feet together, so as to hold anything between them. If the horse wants to seize or hold any substance he must do it with his mouth. The Elephant has a special provision for the purpose of prehension in his trunk, which enables him to provide himself with food by pulling down the branches of trees. The Lion and the Tiger can press their fore paws together sufficiently to enable them to hold their prey, and fix it upon the ground, while they put the head down to it and pull at it and tear it with their teeth; and they are furnished with rudimentary, or half, collar-bones suspended in the flesh of the upper part of the chest; while the little Squirrel, which sits upon its hind legs, and holds up the nuts between its fore paws to be nibbled, has complete collar-bones. So has the flying Bat, the climbing Sloth and the digging Mole. In Birds the collar-bones (fig. 56, AA) are very large; and, for the purpose of giving them greater strength, they are united together in the middle line just above the breast-bone, forming what is commonly called the “merry-thought;” and, as this is not sufficiently strong to resist the force of the powerful muscles which flap the wings and sustain the animal in the air, there are, in addition, stout “side-bones,” called by anatomists “coracoid bones.” These (B) run, from the breast-bone (D), in the same direction as the collar-bones, one, on either side, to the shoulder-blades (C); and they afford even more efficient support to the shoulders than do the collar-bones. The coracoid bones are peculiar to oviparous animals, or nearly so. In some reptiles, as the Crocodile, they quite supersede the collar-bones.