THE HUMAN FOOT ITS FORM AND STRUCTURE FUNCTIONS AND CLOTHING BY THOMAS S. ELLIS CONSULTING SURGEON TO THE GENERAL INFIRMARY AT GLOUCESTER
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http://www.ahcuah.com/ellis/
https://books.google.com/books?id=rO8xXMyXXGkC&pg=PP9
There is an important change which takes place in the great toe, in moving from the position of rest to one of activity, which involves an alteration in the horizontal contour line. Let us suppose that it has become necessary, to have a specially firm foot-hold, that some one sitting quietly in a chair springs suddenly to his feet and puts himself into an attitude of defence. Immediately the great toe leaves its fellows, going over towards the middle line of the body, and leaving a space between it and the second toe. The same action which presses it against the ground causes this movement also, but there is no bending, no flexion — it remains quite straight.
Before going further it should be clearly understood that there is in the great toe an essential difference in the function as well as in the structure from that common to all of the other four. The former serves as a firm solid base from which the body can be propelled onward.
The most prominent on the inner side is the flexor longus pollicis, on the outer the peroneus longus. Those tendons which are deeper are also tightened; the flexor longus digitorum and the tibialis posticus on the one side, and the peroneus brevis on the other. Now all these muscles are strong — their combined strength is enormous — and although they do not act at the same advantage as the calf muscle, which acts on the projecting or lever-like heel, they do exercise a very great influence in bringing the leg and foot towards a continuous straight line, which is the essence of the tip-toe movement. Take the first-named only; the flexor longus pollicis is so strong that it may be trained to bear the weight of the body itself, as in the stage dancer, who will support himself, or more generally herself, literally on the great toe. Though incapable in most persons of anything like such a feat as this, the muscles in question is, in all good feet, very strong.
It will be seen that the effect of tightening, of shortening the tendon of the long flexor muscle is to diminish the distance between the great toe and the point where the tendon passes round the bone of the heel below the ankle. The result of this is to brace up the arch and increase its convexity. But, it should also be understood, the effect of tightening this tendon or cord is to draw it towards a straight line between the point of attachment to the great toe and the point where it passes below the heel. By this agency the joint at the root of the great toe is uplifted, and if the tightness be sufficient to bear the weight of the body, the anterior pillar of the arch literally dances on the tight rope. If, however, the weight of the body, as indicated by the arrow in fig. 28, be sufficient to bear it down, the anterior pillar is, at least, let down lightly. Thus the same agency that assists in raising the body braces up the arch of the foot, and, in lifting the joint at the root of the great toe, relieves it from the pressure against the ground which the weight of the body suddenly thrown upon it would occasion.
As compared with the long flexor muscle, which is common to all the smaller toes, that acting on the great toe alone plays, in supporting the arch, the much more important part. In animals, as in man, the flexor muscle is generally divided into two. — The horse has, in his divided flexor muscle acting on a single tendon, a relic of remote ancestors having two toes and two flexors — But, where all the digits exist, the division of duty is, however varied in arrangement, more evenly distributed than in the case of man, where one division forms the flexor longus pollicis, acting on a single toe. This is a special characteristic. This is one more evidence of the special importance of the great toe in the human foot.
The division of the great toe into two phalanges only, with two flexor muscles, one to each, is effective to hold both down and keep it straight in all its length. Here the advantage of this construction and of the special development to remarkably large size of the first digit is apparent. It forms a firm solid base, much more so than if, like the other toes, it became flexed. Figs. 29 and 30 mark the contrast. In the one case, representing the great toe, a metatarsal bone (a) is shown with two phalanges. Let it be remembered that there is not only a short flexor of the great toe but an abductor and an adductor, one pulling one way and one in the opposite direction, and, like the two reins of a bridle when both are pulled together, they have a joint or collective action. This is the same as that of the short flexor. The three may therefore be regarded as one set of flexor muscles. Their effect, represented by the line 1, is to hold down the first phalanx, acting on it as on a lever, the fulcrum being formed by the joint at the base of the great toe.
On the contrary, as it lies between the points operated on by the two forces indicated by the lines 1 and 2 in fig. 29, it is the point of greatest downward pressure. Thus, the first phalanx being held down, the powerful long flexor, (2) acting on the second, exerts all its influence on a straight great toe.
Before leaving the consideration of the toes, and the manner in which they are acted upon by the muscles, it is desirable to notice that the words flexor and extensor, as applied to those muscles, express that which those corresponding to them do in the hand. They express that which the muscles acting on the toes would do towards them if the toes were used as grasping organs. The words do not express their action in the ordinary function of the feet, in walking.
In this act the flexors of the great toe do not flex it at all: they hold it against the ground at full length. The flexors of the smaller toes do not flex them in the ordinary sense of the word : they do not put them in the position shown in fig. 32, p. 51, but in that shown in fig. 30, where the final phalanx is actually extended on the second. The extensors do not extend the smaller toes: they pull the leg forward, acting on the first phalanges as fixed points, while the second and third are held down by the flexors. Nor does the long extensor special to the great toe, and the portion of the short extensor going to it, have any effect in extending the great toe; they pull upon it while the flexors hold it straight on the ground.