Bones of the Foot
There are 26 bones in the Foot. The hinder 7—called tarsal bones—are short and thick; they form the hinder part of the instep. In front of them lie 5 metatarsal bones, one passing, forwards, from the fore part of the tarsus to each toe. Behind, these are close together, and are connected with the tarsus. As they run forwards they diverge a little from one another; and their anterior ends rest upon the ground, and form the “balls” of the toes. They constitute the fore part of the instep. The remaining 14 bones are the toes. They are arranged in rows, like soldiers in a phalanx, three deep, and are hence called phalanges.
You observe that, although each of the other toes has 3 bones, the great toe has only 2. In this respect, therefore, it is an imperfect, or, rather, an incomplete member. The deficiency does not depend upon a want of length in the great toe; for this is usually as long as the second toe; in some persons it is a good deal longer; and it is always distinctly longer than the outer two toes. The reason for there being only two phalanges instead of three probably is because the great toe is required to be stronger than any of the others; and an additional bone would have tended to weaken it. I have, elsewhere1, given reasons for thinking that it is the middle phalanx which is absent in the great toe.
It is a curious and interesting fact, affording a remarkable illustration of the close adherence to a uniform plan which has been observed in the construction of the various animals, that, in no instance, does this toe contain more than two bones. Even in those creatures, as the Seal (fig. 2), in which it attains to greater length than any of the other sprawling digits, it contains the same number of bones as in man, its extraordinary length being attained by an elongation of the two bones, not by the addition of a third. And in those animals, as certain Lizards (fig. 3), where the number of bones in the other toes is increased to 4 or even 5, the number in the first, or inner, toe is still no more than two. The same rule applies to the fore limb; the number of bones in the inner digit, which, in man and monkeys, is called the “thumb,” is in no case more than two. In some animals, as will be mentioned again, there is only one bone in this digit, and in some the digit is wanting altogether; but in none does it contain more than two bones.
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.
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.