Part 3

This reminds me of a still more remarkable instance of adherence to a particular number of bones. In the mammalian group of animals the neck, with only one or two exceptions, contains seven bones, neither more nor less. Whether it be the long neck of the GIRAFFE, or the short neck of the MOUSE, the BAT, or the PORPOISE, each consists, like the neck in MAN, of seven bones. For what reason a particular number should be thus rigidly observed, it is not easy to say.

Of the seven tarsal bones the uppermost (fig. 1) is called the astragalus, from a supposed resemblance to a die. It is the middle bone of the instep. Above, it is jointed with the leg-bones; behind, it is connected with, and rests upon, the heel-bone, which is the largest bone in the foot. The bone which lies immediately in front of the astragalus, and supports it in this direction, is called the scaphoid, or boat-like, bone. In front of it are three wedge-bones, each of which is connected with one of the metatarsal bones of the inner three toes. On the outer side of the wedge-bones, connected with the metatarsals of the two small toes, and locked in between them and the heel-bone, is the cuboid bone.

I must confine my remarks chiefly to the human foot. Still the anatomy of man derives so much interest from being studied in connexion with that of the lower animals, and is so much more instructive when this is done, that I cannot forbear diverging, here and there, to make a few comparisons. Let me, for a moment, draw your attention to a similarity, in general construction, which exists between the lower limbs of man, and the hinder limbs of other animals. And the comparison may be extended to the fore limbs; for however diverse may be the appearance and the mode of action of the limbs in different animals, whether they be terminated by hands or by feet, whether they move upon the ground or ply in air or water, whether they be attached to the head, as are the front fins in many fishes, or, as is more common, be situated at the fore and hinder parts of the trunk, the same plan is traceable in all.

Great, indeed, is the variety of detail in nature. It is everywhere observable. No two things, however near their resemblance, are precisely alike. Yet, as I have before said, there is a remarkable adherence to unity of plan. One star differs from another star in glory, yet all appear fashioned in the same manner, and subject to the same laws. There are almost infinite varieties in the vertebrate kingdom. Each animal exhibits its own peculiarities; yet they are all formed in the same manner, and are developed upon one fundamental pattern, diverging from it in different ways according to the requirements of each. Again, though the several parts of the same animal differ from one another; yet in the skeleton the same bones which exist in one part may, as a general rule, be traced in other parts and in other animals. The bones which make up the pelvis in man are repeated in his shoulder, and, even, in his skull; and they may be recognised in the pelvis, in the shoulder, and in the skull, of all other vertebrate animals, with few exceptions. They undergo, it is true, great varieties in shape and size; but they can be shown to be the same, or, in the language of anatomists, to be “homologous.” It is highly interesting to the anatomist to trace the same bone through the different parts of the same animal, and through the various animals of the vertebrate series, and to observe the modifications which it undergoes in order to adapt it to the multiform mechanism of the several classes, to observe it sometimes dwindling, or even vanishing, and then, it may be, reappearing under some new conditions.

Human Leg.]

Horse’s Leg.]

I must, however, resist the temptation to wander into this attractive field. It will suffice to take an illustration by a comparison of the bones of the human lower limb with those of the hind limb of the Horse. This may be easily done by the aid of these drawings (figs. 4 and 5) in which the two limbs are placed side by side, and the corresponding bones are marked with the same letters. Notwithstanding the many points of difference the same plan will be recognised in each. There is in each the thigh(C), the leg(E), and the foot, with the tarsal and metatarsal(G) bones, and the phalanges(H, I, K). But in the HORSE two of the digits (the marginal ones, that is, the great toe and the little toe) are wanting, two are rudimentary, and the remaining one, which corresponds with the middle toe of man, in length, size, and strength, more than makes amends for the deficiency of the others. The lowermost bone, or terminal phalanx, of this huge toe, called the coffin-bone(K), is encased in the hoof, which corresponds with the human nail, and is the only part of the foot that rests upon the ground.

In MAN the whole weight of the body has to be borne upon two feet; often it is balanced upon one. The foot is, consequently, spread out; and all the bones, from the heel to the tips of the toes, are made to form the basis of support upon the ground. The HORSE, on the contrary, having no hands, but four feet, does not require so great breadth in each foot; and the opportunity is taken to narrow the foot, and to lengthen it so as to give fleetness. The end is attained by suppressing some of the toes, by elongating one far beyond the others, and enduing it with such strength as to enable it to carry the requisite weight upon the tip of the last phalanx. The heel(F) is raised high above the ground and becomes the “hock.” To speak of a horse kicking with his heels is, therefore, about as correct as to say, that he breaks his knees. His knee, as you perceive by the position of the “knee-cap”(D), is high up in the hind limb, near his body, quite out of harm’s way in a fall. The fact is, that he kicks with his toes; and, when he falls, he cuts the skin over the part in his fore limbs, which corresponds with the back of our wrists.

In the upper segment, or thigh, the difference between the two limbs is seen to be, to a certain extent, the reverse of what it is below. That is to say, whereas, in the HORSE, the toe is elongated and thickened, so as greatly to exceed the corresponding part of the human limb; in MAN the thigh-bone is elongated, so as to be double the length of that of the horse; the thigh-bone in man is also placed more vertically, nearly in the plane of gravity of the trunk. The horse’s thigh-bone slants forwards and outwards, which gives the muscles great power by causing them to run more at right angles between their points of attachment; and this arrangement increases the strength of the animal in drawing weights, and facilitates springing. A man cannot spring without first bending the limbs a little; whereas a horse, or a goat, can spring, at once, from the position in which it is standing.

To revert to the anatomy of the Human Foot.

The Arch of the Foot.

The seven tarsal and the five metatarsal bones--that is, the twelve bones of the instep--are arranged and jointed together so as to form an arch from the point of the heel to the balls of the toes. This is called the “plantar arch,” from the Latin word planta, the sole of the foot. The astragalus forms the summit, or key-bone, of the arch. It receives the weight from the leg, and transmits it, through the hinder pillar of the arch, to the heel, and, through the front pillar of the arch, to the balls of the toes.

The drawing represents a section, from behind forwards, of the lower end of the leg-bone, and of the bones lying along the inner side of the plantar arch. Behind it extends through the heel-bone, and in front through the great toe. It exhibits the arrangement of the fibres and plates in the interior of the bones, and shows that the greater number of them, in each bone, follow the direction of the two pillars of the arch; that is to say, they descend from the summit of the arch where it supports the leg-bone, backwards and downwards, to the heel, and, forwards and downwards, to the balls of the toes. Their arrangement is, therefore, such as to give resisting strength to the bones in the directions in which it is most required.

You may think that the arch of the foot would have been a much simpler structure, as well as stronger, if it had been composed of one bone instead of several. But it must be remembered that it would, then, have been liable to be cracked and broken by the sudden and violent manner in which, during running and jumping, the weight of the body is thrown upon it. Moreover, the several bones, where they touch one another, are covered with a tolerably thick layer of highly elastic gristle or cartilage (represented by the clear line left in the drawing along the contiguous edges of the bones); and this provision, together with the slight movements which take place between these bones, gives an elasticity to the foot and to the step, and serves to break the jars and shocks which are caused by the sudden contact of the foot with the ground.

This last is a very important point; and we find numerous contrivances in different parts of the body to protect the brain and other delicate organs from jars. So efficient are these contrivances, and so exact is the adaptation of the mechanism of the limbs and the trunk to the texture of the internal organs, that, while these are in a healthy state, we are able to run, to jump, and to leap from a considerable height, without inconvenience. But, if the organs be inflamed, or if the nervous system be over sensitive, as in common headache, the provisions, which are calculated for the normal state, are insufficient; ordinary movements are then painful, and to jump is intolerable.

The muscles play a very essential part in this work. First, they place the limbs in the most favourable position. Thus, when we alight upon the ground, from a height, we always contrive to do so with the knees and hips a little bent, so that the limbs readily yield at the joints, and act as springs to break the jar. Elderly persons commonly keep the limbs bent, even when walking quietly along. They do this because they need all the benefit which position will afford to make amends for the loss of elasticity consequent on the thinning and drying of the cartilages, and other changes that take place in the body with advancing years. Secondly, the muscles brace the limbs and joints in the position in which they have placed them. We experience the effect of the want of this salutary influence when we kick against an unseen object, or fall suddenly, or receive any blow or shock for which we are unprepared. How disagreeable, to say the least, it is to make the step for an additional stair when we have arrived at the top of a staircase, or, still worse, to meet with an unseen stair when we think that we have got to the bottom.

You perceive from the drawing (fig. 6) that there is a great difference between the two pillars of the plantar arch. The hinder pillar is comparatively short, and narrow, and descends suddenly, almost in a vertical direction, from the ankle, to the ground; and it is composed of only one bone--the heel-bone--which is jointed directly with the astragalus: whereas the fore pillar is longer and broader, is composed of several bones jointed together, and slopes much more gradually to the ground. There is, therefore, far less elasticity in the hinder part of the foot than in the fore part. Hence, when we descend from a height upon the ground, we always alight upon the balls of the toes, and thus gain the advantage which the several bones and joints afford in breaking the shock. If, after going up stairs this evening, you take the trouble to come down again, you will find that you alight upon each stair on the balls of the toes and experience no inconvenience, however quickly the descent is made. But, if you change the mode of proceeding, and descend upon the heels, the feeling will be by no means agreeable; and the various organs of the body, being disturbed from their accustomed repose, will raise such remonstrances against your infringement upon nature’s ways, that you will scarcely be able to continue the experiment. Proportionately more distressing is the sensation caused by jumping from a chair upon the heels. Indeed, this is not done altogether without risk; and the trial of it is scarcely to be recommended to persons who have attained to that sober period of life at which we are willing to concede that, in some things, nature is wiser than ourselves. Only a short time since I saw a gentleman, who, in jumping down some steps into a back yard, accidentally came upon his heels, and jarred one hip so severely that he was confined to his sofa for several days in consequence.

But, you may say, “in walking we do place the heel upon the ground first and experience no inconvenience.” True, because the force with which the foot descends in walking is very slight; and the weight is directed upon the heel, obliquely, in such a manner as to bring the toes very quickly to the ground, and really to throw nearly the whole force in that direction. Moreover, you may observe that when we walk, the weight of the body is partly sustained by the fore part of the one foot till the whole of the other foot is on the ground. I will, however, revert to the disposition of the feet in walking and running presently.

The arch of the foot has to bear great weight and at great disadvantage; and there is very little in the shape of the bones to maintain its integrity. Indeed, they all fall asunder when the other structures are removed, the key-bone dropping through of its own weight. And the same thing may be remarked throughout the skeleton. Wherever two or more bones move upon one another, their surfaces are so constructed that they do not hold together without some assistance from the soft parts. There are joints in the body which we call “hinge-joints,” and others which we call “ball-and-socket joints;” but in none of them is there such a holding and locking of one part in the other as you have in the hinge and the ball-and-socket of the mechanic. In every case the bones are held together, not by their own shape, but by ligaments and muscles. Consequently, any one of the bones may be dislocated from those next it without breakage; and when the muscles and ligaments are cut through, or have been destroyed by maceration, all the bones, between which any movement was possible during life, separate from one another.

Not only is this so, but in no instance are the movements of joints limited simply by the shape of the bones--that is to say, they are never brought to a stop by a part of one bone coming into contact with the edge of another. Such a contact would have caused a sudden check; and this would have been attended with more or less jar and with some danger of chipping and breaking the articular edges. The range of movement of a joint is always regulated by the ligaments or the muscles, not, directly, by the bones; and the restraint thus imposed upon the movements is brought to bear, not suddenly, but gradually; somewhat like the effect of the “break” upon a railway-train; while the cartilages between the bones may be compared with the “buffers” between the carriages.

It is chiefly by means of strong LIGAMENTS, or sinewy bands, passing from bone to bone, that the shape of the plantar arch is maintained and the movements of the bones upon one another are regulated and limited. These ligaments are numerous; but I will mention only two.

One, the Plantar Ligament (A, fig. 7), of great strength, passes from the under surface of the heel-bone, near its extremity, forwards, to the ends of the metatarsal bones; in other words, it extends between the lowest points of the two pillars of the arch, girding, or holding, them in their places, and preventing their being thrust asunder when pressure is made upon the key-bone (D); just as the “tie-beam” of a roof resists the tendency to outward yielding of the sides when weight is laid upon the summit. The ligament, however, has an advantage which no tie-beam can ever possess; inasmuch as a quantity of muscular fibres are attached along the hinder part of its upper surface. These instantly respond to any demand that is made upon them, being thrown into contraction directly the foot touches the ground; and the force of their contraction is proportionate to the degree of pressure which is made upon the foot. Thus they add a living, self-acting, self-regulating power to the passive resistance of the ligament. In addition to its office of binding the bones in their places, the ligament serves the further purpose of protecting from pressure the tender structures--the blood-vessels, nerves and muscles--that lie above it, in the hollow of the foot, under the shelter of the plantar arch.

Another very strong ligament (B in the wood-cut) passes from the under and fore part of the heel-bone (F) to the under part of the scaphoid bone (E). It underlies and supports the round head of the astragalus, and has to bear a great deal of the weight which is transmitted to that bone from the leg. It does not derive the same assistance from a close connexion with muscular fibres as the ligament just described; but it possesses a quality, which that and most other ligaments do not have, viz. elasticity. This is very important, for it allows the head of the key-bone (D) to descend a little, when pressure is made upon it, and forces it up again when the pressure is removed, and so gives very material assistance to the other provisions for preventing jars and for giving ease and elasticity to the step.

A glance at the drawing will show you that here is a weak point in the foot. The head of the key-bone receives great weight from the leg, but is comparatively unsupported; and there is a considerable strain upon this part when the heel is being raised in walking. Moreover, a good deal of movement takes place between the key-bone (D) and the scaphoid bone (E), more than between any other two bones of the instep; and freedom in the range of movement is generally attended with some sacrifice of strength. The strong elastic ligament comes in therefore with peculiar advantage at this point; and it is underlaid, and additional support is afforded exactly when it is most required, by the tendon (b in fig. 12) of a strong muscle, the especial office of which is to assist in raising the heel and bending the instep, and which runs, from the back of the leg, behind the inner ankle, to the scaphoid bone.

Weak Ankle and Flat-foot.

In spite, however, of the thick elastic ligament and the strong tendon just mentioned, the joint between the astragalus or key-bone and the scaphoid bone still remains a weak point. The head of the key-bone, from being insufficiently supported or from being overweighted, is very apt to descend a little below its proper level; the consequence of which is that the plantar arch is lowered and the foot is flattened; and the more the foot is flattened the weaker it necessarily is, because the position of the bones then becomes less and less favourable for bearing weight, and an increasing strain is thus incurred by the ligaments and muscles. Hence the foot and ankle feel weak; and the weakness is especially felt when the person endeavours to raise the heel, so as to mount upon the balls of the toes, in walking. For the performance of that movement with ease and steadiness a well-formed plantar arch is essential; and the person, whose feet are defective in the manner we are considering, can never walk with a bold, firm step. The movement in him may be better described as a shuffling from one foot on to the other, than as a walk. To this I will recur again when I come to speak more of walking. The defect, when slight in degree, is commonly called “weak-ankle;” when more decided it is called “flat-foot,” because the sole is then nearly, or quite, flat. The head of the key-bone, under such circumstances, may even bulge downwards and inwards, and form a prominence on the inner side of the sole, so as to give more or less convexity to the line on the inner side of the foot, which should be concave.

The representation of “flat-foot” here shown was drawn from the foot of a labouring man in this county. He said he believed the deformity was due to his having worn thick tight shoes when he was a growing boy. He is most likely right in his opinion; for tight or ill-fitting shoes, cramping the feet and preventing the proper growth of the bones and the free play of the muscles, are a common cause of this evil. This is so especially among the agricultural class, whose feet are, from an early period, enclosed in stiff unyielding leather cases that are enough to mar nature’s best efforts to construct a plantar arch.

The same drawing shows that flat-foot is not the only deformity for which “high-lows” are answerable. Besides the almost total want of calf, which is due to the wearer being obliged to hobble along, whole-footed, with short feeble steps, it will be seen that the great toe has not been allowed to assume its natural straight line, but has been squeezed athwart the other toes, so as to be almost at a right angle with the foot. No room at all is thus given for the second toe; it has been driven quite out of the field, and has been obliged to hide itself by bending down under the other toes. This is no uncommon state of things. Frequently it is attended with the formation of a painful bunion upon the prominent inner side of the ball of the great toe; and, in addition, there is sometimes a corn upon the first joint of the second toe, which is a source of so much inconvenience that I have known many sufferers glad to get relief by parting with the toe.