Extensor muscle

“ In the cat, there is a fourth tendon, which passes to the index-finger, so that the name common extensor of the four external digits is in this case legitimate, and the lateral extensor of the phalanges is also a common extensor, as is the anterior extensor of the phalanges, or common extensor of the digits.
In the pig, the tendon, which is single, is inserted into the external digit, for which reason it has received the name of the proper extensor of the small external digit. This muscle is, then, really the homologue of that which exists in the human species. ”

“ As the extensor muscles are all paretic, this can only be effected by means of the muscles of the upper extremities and of the weight of the body, which the arms compel to serve as a motor force. Thus, from a recumbent position the patient rolls upon his hands and knees: then, grasping the knee, he lifts the leg upright with the foot planted on the ground. The thighs remain strongly flexed, the trunk bent forward over the thighs. The action of grasping the thighs above the knees, which is so characteristic, serves to extend them by a double mechanism. ”

“ A fourth muscle exists, which veterinary anatomists include in the study of the three portions of the triceps which we have just been discussing, in giving it the name of small extensor of the forearm. But, as this muscle is no other than the anconeus, and as, in human anatomy, we describe the latter, according to custom, in connection with the forearm, it is when on the subject of the latter that we will concern ourselves with it. ”

“ That the second condition may be realized, there must be such a development of the extensor muscles on the back of the body as will be sufficient to antagonize the flexor muscles on the front of the body. ”

“ There are no essential alterations of muscle or tendon except those secondary to the contraction of the joint—namely, an undue tension and prominence of the extensor tendon over the metatarso-phalangeal articulation, and an adaptive deficiency of length in the flexors, which are prevented by the permanently bent state of the articulation from keeping pace in growth with the osseous structures. ”

“ In the upper part of the leg the tibialis anticus, A, Plate 67, Figure 2, and extensor-communis muscle, B, are adherent to the fascia which covers them, and to the intermuscular septum which divides them. In the lower part of the leg where these muscles and the extensor pollicis, C, terminate in tendons, a b c, they are readily separable from one another. The tibialis anticus lies along the outer side of the tibia, from which, and from the head of the fibula and interosseous ligament, it arises tendinous and fleshy. This muscle is superficial in its whole length ”

“ This belief is founded on what I regard as an erroneous assumption, viz., that muscles have only the power of shortening, and that when one muscle, say the flexor, shortens, it must drag out and forcibly elongate the corresponding extensor, and the converse. This would be a mere waste of power. Nature never works against herself. There are good grounds for believing, as I have stated elsewhere,14 that there is no such thing as antagonism in muscular movements; the several muscles known as flexors and extensors; abductors and adductors; pronators and supinators, being simply correlated. ”

“ Thus, from the foot up to the spinal column the morbid imminence is pronounced on the side of the extensor muscles. The liability to invasion on the part of the flexors is greatest at the foot, where dorsal flexion is early impeded, and diminishes upward toward the abdomen.
Most important for the theory of the disease is the fact that the hypertrophic appearance of the muscles is never accompanied by even a transitory period of increased strength.28 Some degree of paresis usually precedes the hypertrophy, and becomes intensified when this sets in. ”

“ One of the toes becomes pressed downward between two others. This over-stretches the extensor muscles and tempts the unbalanced flexors to contract. As the extensor muscles become, after a time, unable to work in the constantly bent toes, they atrophy to some extent and then the flexor muscles pull the toe farther and farther down until there is no possibility of its being straightened at all. Now, if the flexor tendons are cut and the toe straightened the atrophic extensor muscles will not hold it in that position, and when the flexors grow together the old condition will reassert itself. ”

“ In the process of repair, one or both ends of the muscle or tendon may become fixed by adhesions to adjacent structures, and if the distal portion of a muscle is deprived of its nerve supply it may undergo degeneration and so have its function impaired.
Rupture of a muscle or tendon is usually the result of a sudden, and often involuntary, movement. As examples may be cited the rupture of the quadriceps extensor in attempting to regain the balance when falling backwards; of the gastrocnemius, plantaris, or tendo-calcaneus in jumping or dancing ”

“ If the body, when projecting under the integuments, be gently compressed, it yields to the pressure, changes its situation, and, according to the impression it has received, moves either to the internal or the external side of the joint, or reciprocally from one side to the other, passing also behind the rotula, behind the inferior ligament, or sometimes behind the tendon of the extensor muscles. ”

“ Consider for a moment the nicety with which the powers of these muscles must be balanced, and the harmony which must subsist between them in their various operations. When we are closing the hand, if the extensor muscles did not gradually yield to the flexors—if they gave up their hold all at once, the hand, instead of closing with gentleness and ease, would be jerked together in a sudden and most uncomfortable manner. ”

“ The chief adductor muscle of the thumb (extensor metacarpi pollicis) is particularly powerful; the other extensors of the thumb are very weak, and work under unfavourable physical conditions, but are supported in their action by the strong abductor muscle. The muscles of the abductor, opponens and flexor brevis, in the complicated work thrown on the thumb in manipulation, are much exerted, so that the effects of overexertion show themselves first in this region. ”

“ For instance, if the extensor muscles of the arm are lightly touched, the arm stiffens immediately, and is only made flexible again by a hard rubbing of the same muscles. The nerves also react in a similar manner. The irritation of a nerve trunk not only contracts all the small nerves into which it branches, but also all those muscles through which it runs. ”

“ On enrolling, the sternites of all segments are pulled forward and the tergites backward. In straightening out, the reverse process takes place. The areas available for muscular attachment [93] are so disposed as to indicate longitudinal flexor and extensor muscles rather than short muscles extending from segment to segment. Indeed, the tenuity of the ventral membrane is such as to preclude the possibility of enrollment by the use of muscles of that sort, while powerful longitudinal flexors could have been anchored to cephalon and pygidium. ”

“ A leap is effected chiefly by the bending of the hind limbs so as to make sharp angles at the joints, and then suddenly straightening them; as any one may see on watching a cat leap on to the table. The first required change, then, is increase of the large extensor muscles, by which the hind limbs are straightened. Their increases must be duly proportioned, for if those which straighten one joint become much stronger than those which straighten the other joint, the result must be collapse of the other joint when the muscles are contracted together. ”

“ The extensor muscles, not being at all compressed, will act with their whole force on the upper fragment, and, on the slightest effort of the patient, overcome the resistance of the bandage, the action of which, being oblique with respect to the fragment, is inconsiderable, unless it be drawn very tight, and thus a displacement will again occur. This obliquity of the turns of the roller obliges the surgeon, either to draw it very tight, in which case a swelling is inevitable, or to make it but moderately tight, and then the apparatus will be insufficient to resist the action of the muscles. ”

“ The tendons constantly exposed to the contraction of these organs, are at every instant placed between the strong power that they represent and the more or less considerable resistance situated at the extremity of the muscles, &c. Such is this resistance, that it is often greater than that of the bones themselves. We know that by muscular efforts alone, the patella, the olecranon process and the os calcis are sometimes broken; now this could not happen, if the extensor tendons, which corresponded to these different bones, were of a texture that could be more easily torn. ”

“ There are but few motions in the economy that are simple, but few muscles that can contract separately. Almost every sort of contraction supposes another, and for this reason; the two points to which a muscle is ordinarily attached are both capable of being moved; if one of them was not fixed, both would then be put in motion when the muscle contracted; thus in the contraction of its extensors, the leg if it was not fixed would approach the foot as much as the foot approached the leg ”

“ The extensor tendons, because of the nature of their function, are very seldom strained; they are often bruised and occasionally divided, but unlike this condition in the flexors, tendinitis of the extensors is of rare occurrence. ”