and in old age far less. Twenty-four ribs bound the chest laterally, twelve on each side, and most of them are connected by cartilages with the breastbone. In the girdle which supports the shoulder, two bones are always distinguishable as the scapula and the clavicle. The pelvis, to which the legs are attached, consists of two separate bones called the ossa innominata in the adult; but each os innominatum is separable into three (called pubis, ischium, and ilium) in the young. There are thirty bones in each of the arms, and the same number in each of the legs, counting the patella, or knee pan.

All these bones are fastened together by ligaments, or by cartilages; and, where they play freely over one another, a coat of cartilage furnishes the surfaces which come into contact. The free surfaces of those articular cartilages which enter into a joint, again, are lined by a delicate synovial membrane, which secretes a lubricating fluid-the synovia.

15. Though the bones of the skeleton are all strongly enough connected together by ligaments and cartilages, the joints play so freely, and the centre of gravity of the body, when erect, is so high up, that it is impossible to make a skeleton, or a dead body, support itself in the upright position. That position, easy as it seems, is the result of the contraction of a multitude of muscles which oppose and balance one another. Thus, the foot affording the surface of support, the muscles of the calf (Fig. 2, I) must contract, or the legs and body would fall forward. But this action tends to bend the leg; and to neutralize this and keep the leg straight, the great muscles in front of the thigh (Fig. 2, 2) must come into play. But these, by the same action, tend to bend the body forward on

FIG. 2.-A DIAGRAM ILLUSTRATING THE ATTACHMENTS OF SOME OF THE MOST IMPORTANT MUSCLES WHICH KEEP THE BODY IN THE ERECT POSTURE.

I. The muscles of the calf. II. Those of the back of the thigh. III. Those of the spine, which tend to keep the body from falling forward.

1. The muscles of the front of the leg. 2. Those of the front of the thigh. 3. Those of the front of the abdomen. 4, 5. Those of the front of the neck, which tend to keep the body from falling backwards. The arrows indicate the direction of action of the muscles, the foot being fixed.

the legs; and if the body is to be kept straight, they must be neutralized by the action of the muscles of the buttocks and of the back (Fig. 2, III).

The erect position, then, which we assume so easily and without thinking about it, is the result of the combined and accurately proportioned action of a vast number of muscles. What is it that makes

them work together in this

way ?

16. Let any person in the erect position receive a violent blow on the head, and you know what occurs. On the instant he drops prostrate, in a heap, with his limbs relaxed and powerless. What has happened to him? The blow may have been so inflicted as not to touch a single muscle of the body; it may not cause the loss of a drop of blood and, indeed, if the "concussion," as it is called, has not been too severe, the sufferer, after а few moments of unconsciousness, will come to himself, and be as well as ever again. Clearly, therefore, no permanent injury has been done to any part of the body, least of all to the muscles, but an influence has been exerted upon a something which governs the muscles. And this influence may be the effect of very subtle causes. A strong mental emotion, and even a very bad smell, will, in some people, produce the same effect as a blow.

These observations might lead to the conclusion that it is the mind which directly governs the muscles, but a little further inquiry will show that such is not the case. For people have been so stabbed, or shot in the back, as to cut the spinal cord, without any considerable injury to other parts: and then they have lost the power of standing upright as much as before, though their minds may have remained perfectly clear. And not only have they lost

the power of standing upright under these circumstances, but they no longer retain any power of either feeling what is going on in their legs, or, by an act of their volition, causing motion in them.

17. And yet, though the mind is thus cut off from the lower limbs, a controlling and governing power over them still remains in the body. For, if the soles of the disabled feet be tickled, though no sensation will reach the body, the legs will be jerked up, just as would be the case in an uninjured person. Again, if a series of galvanic shocks be sent along the spinal cord, the legs will perform movements even more powerful than those which the will could produce in an uninjured person. And, finally, if the injury is of such a nature that the cord is crushed or profoundly disorganized, all these phenomena cease; tickling the soles, or sending galvanic shocks along the spine, will produce no effect upon the legs.

By examinations of this kind carried still further, we arrive at the remarkable result that the brain is the seat of all sensation and mental action, and the primary source of all voluntary muscular contraction; while the spinal cord is capable of receiving an impression from the exterior, and converting it not only into a simple muscular contraction, but into a combination of such actions.

Thus, in general terms, we may say of the cerebrospinal nervous centres, that they have the power, when they receive certain impressions from without, of giving rise to simple, or combined, muscular contractions.

18. But you will further note that these impressions from without are of very different characters.

C

Any part of the surface of the body may be so affected as to give rise to the sensations of contact, or of heat or cold; and any or every substance is able, under certain circumstances, to produce these sensations. But only very few and comparatively small portions of the bodily framework are competent to be affected, in such a manner, as to cause the sensations of taste or of smell, of sight, or of hearing: and only a few substances, or particular kinds of vibrations, are able so to affect those regions. These very limited parts of the body, which put us in relation with particular kinds of substances, of forms of force, are what are termed sensory organs. There are two such organs for sight, two for hearing, two for smell, and one, or more strictly speaking two, for taste.

19. And now that we have taken this brief view of the structure of the body, of the organs which support it, of the organs which move it, and of the organs which put it in relation with the surrounding world, or, in other words, enable it to move in harmony with influences from without, we must consider the means by which all this wonderful apparatus is kept in working order.

All work, as we have seen, implies waste. The work of the nervous system and that of the muscles, therefore, implies consumption either of their own substance, or of something else And as the organism can make nothing, it must possess the means of obtaining from without that which it wants, and of throwing off from itself that which it wastes; and we have seen that, in the gross, it does these things. The body feeds, and it excretes. But we must now pass from the broad fact to the mechanism by which the fact is brought about.