To the twelve vertebrae of the back there are attached on each side twelve pairs of thin curved bones called ribs. These bones are attached not one to each vertebra, but one between each two, i.e., each of these bones is attached to two of the vertebrae of the back and to the disc between them. They are not attached so that they cannot move at all, but are so attached, by means of what we call a true joint, that they can. be moved pretty freely.

A substance, softer than bone, which we call cartilage or gristle, is found at their other ends. These cartilages or gristles are attached in the case of the first seven pairs of ribs to a bone in the front of the chest called the breast-bone or sternum. The cartilages of the next three are attached to one another, and the other two ribs are not attached in front at all These ribs and sternum form part of the walls of a kind of cage called the chest cavity, and protect the soft parts within the cavity of the chest.

Lastly, there are the bones of the Limbs or Extremities.

In the upper extremity there is, in the first place, a triangular bone which goes by the name of the shoulder-blade. This is situated at the upper part of the back of the chest, and is not directly fixed to the vertebral column at alL In the second place, the collar-bone which connects the shoulder-blade with the sternum or breast-bone.

In the upper limb, after these two bones, comes a long bone called the humerus, which is the bone of the arm proper. This bone has its globular head fitted to a shallow cavity in the shoulder-bone.

Thus the upper limb is only very indirectly connected with the vertebral column, because the main bone of the arm is joined to the shoulder-blade, and this, by means of the collar-bone, to the breast-bone, which is connected to the vertebral column by means of the ribs and cartilages of the ribs. In the lower limb it is very different : instead of the shoulder-blade and collar-bone, we have one bone on each side, which is called the innominate bone, and these bones, so far from being indirectly attached to the spinal column, are firmly attached, one on each side, to the bone that we have bofore referred to as being made of five vertebrae-viz. the sacrum,-and they are joined together in front; so that it will be seen that while the upper limbs are attached to bones which allow of a great amount of movement, the lower limbs are attached to bones which are very firmly fixed, and, in fact, support the vertebral column itself. In each of these two bones there is a deep cavity which receives the head of the main bone of the leg, called the femur, and you will note how admirably this construction is adapted for sustaining the body: one strong bone on each side, with the vertebral column wedged in between them, and the main bone of each leg stuck into a deep hollow in one of these strong bones. Another thing to be noted, too, is, that whereas the main bone of the arm is straight, and its head fits quite loosely into a slight cavity at the end of the shoulder-blade, the thigh-bone is bent at an angle, and its head fits into a deep pit, so that the two thigh-bonesr on account of the angles at which they are bent, form an arch with the bones in which they are set, and- the lower part of the vertebral column is wedged in, as it were, at the crown of this arch.

We will now take the remainder of the upper limb and the remainder of the lower limb. In the fore-arm there are two bones, and in the fore-leg there are two bones; so far they resemble one another. After these two bones in the fore-arm comes a set of small bones called the wrist-bones, eight in number, and there are, likewise, in the lower limb a set of small bones which are called the ankle-bones, seven in number. In the upper extremity, after the wrist-bones, come tKe bones in the hand, five in number, and after them bones in the fingers, three in each finger and two in the thumb. In the lower extremity, after the ankle-bones, we have the bones in the foot, five in number, and then the bones in the toes,, three in each toe, except the great toe, in which there are two; so that it will be seen that in the upper and lower extremities there are considerable resemblances in the way in which they are built up, as to the number and arrangement of their bones, at any rate.

But let us look a little further. The upper limb is one which requires the greatest possible amount of movement; it is a prehensile member, and note how this is provided for. The bones of the fore-arm are called the radius and the ulna. When the arm is hanging down with the palm of the hand forwards, the radius is on the outer side of the fore-arm and the ulna on the inner. The main bone of the arm is joined to the ulna. The radius has a disc-shaped head, rather like a thick gun pellet, which is capable of moving in a groove on the inner side of the head of the ulna. The lower end of the radius is much larger than the upper end. To the lower end of the radius or outside bone of the arm the first four bones of the wrist are joined,and the other four bones join on to them, and the hand bones are joined to these, so that the hand is attached, by means of the wrist, to the end of this radius or outer bone 9f the arm, and has very little to do with the other bone, whereas the other bone is joined on to the main bone of the arm. Therefore, when the head of the radius is turned round in the groove of the ulna, it carries the hand with it, because the hand is attached to it, and so the hand is turned round.

In the lower limb, between the knee and the ankle, there are two bones, the inner one, a very strong bone, called the tibia, on to which the lower end of the thighbone joins, and the other called the fibula, a very thin bone which rests along on the outer side of it. There is no turning round between these two bones at all, and so far from the fibula being joined on to the ankle as the radius is joined on to the wrist, it is especially the tibia, the same one that is joined on to the thigh-bone, that joins with the ankle.

Now the hand is joined on to the outside bone of the arm in a straight line, and it is joined on comparatively loosely, so that you can move the hand very rapidly in many directions, as required, but, on the other hand, the foot is joined on to the bones of the leg at right angles. When the foot is planted upon the ground in a horizontal position these bones are in a vertical position, at right angles to the foot.

The bones of the fore-leg are joined to one bone among the ankle-bones (not to a row, as in the wrist), and another of the ankle-bones projects backwards and so lengthens the basis of support, forming the heel; so it will be seen that in the lower limb the bones are arranged in such a manner as to bear weight, while, on the other hand, the bones of the upper limb and hand are arranged so as to allow the greatest amount of movement. Further, the bones of the ankle and foot are disposed in an arch, thus showing that in the construction of the foot itself you have the strongest construction that we know of for supporting the weight of the body.

Thus we find this construction in the foot, in the pelvis, and in the cranium, the bones of the skull being so arranged in order to protect the brain.