Extraocular muscle

“ The other two are called oblique muscles, one of which, with its long tendon passing through a cartilaginous loop, acts upon the principle of the fixed pulley, and turns the eye in a direction contrary to its own action. When the external muscle becomes too short, the eye turns out; but if the internal muscle is unduly contracted, the eye turns inward, toward the nose. One eye is sometimes turned up or down, but this is of less frequent occurrence. ”

“ It is a brief extension of the limb at the knee-joint, due to a simple contraction of the extensor muscle, elicited by a tap or other short mechanical stimulus applied to the muscle fibres through the tendon of the muscle. The jerk is obtainable only from muscle fibres possessed of neural tonus. If the sensory nerves of the extensor muscle be severed, the “jerk” is lost. The brevity of the interval between the tap on the knee and the beginning of the resultant contraction of the muscle seems such as to exclude the possibility of reflex development. ”

“ Naturally, as Neal has pointed out, they have nothing to do with the eye-muscles; the superior oblique muscle is plainly in its true place entirely apart from these velar muscles, which form the foremost group of the segmental tubular muscles. They pass into the anterior part of the velar folds and run round to the ventral side just in the same way as does the posterior group. This anterior group of tubular muscles represents the veno-pericardial muscle of the segment immediately in front of the opercular, i.e. the metastomal segment, and is the foremost of these veno-pericardial muscles. ”

“ It is only by reason of the homology of situation with the corresponding muscle in man that we give the name under which we are studying it; indeed, its structure is different, for it does not present the long, broad, aponeurotic tendon which, in its superior part, characterizes this muscle in the human species.
It arises above from the inferior surface of the ischium, and from the tuberosity of the same bone. In the pig, and especially in the horse, it passes further upwards, to arise from the aponeurosis of the coccygeal muscles. ”

“ Then in fact the contraction of each muscle serves, both to cause a motion below in the moveable part to which it is attached, and to strengthen above the fixed point of the neighbouring muscles which contract at the same time with it.
Every long muscle is in general thicker in its middle than at its extremities, a form which arises from the manner of the insertion of the fleshy fibres, which arising above and terminating below, some successively below others, are so much the less numerous as we approach nearer each extremity, whilst in the middle they are all found in juxta-position. ”

“ 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. ”

“ The muscle fibers contain innumerous myofilaments of variable thickness that cause the muscle to contract or expand. There are several parallels to the smooth muscle of vertebrates: like these, the echinoderm smooth musculature is made up of fusiform cells [30] , and acetylcholine acts as muscle contractant, while nitric oxide and neuropeptides serve as muscle relaxants [31] . Stauber [15] as well as Dolmatov and colleagues [29] have shown that the compass elevator, retractor, protractor, and postural muscles constitute true subepithelial muscles derived from a stratified myoepithelium. ”

“ 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 ”

“ 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 ”

“ One, the quadratus or bursalis muscle, arises from the hinder surface of the eyeball, and forms with its narrow margin, which is directed towards the optic nerve, a pulley for the long tendon of the pyramidalis muscle. This arises from the nasal surface of the ball, and its tendon passes into the somewhat imperfectly transparent nictitating membrane. The quadrate muscle adjusts the motion, and prevents pressure upon the optic nerve; during the state of relaxation of both muscles the nictitans withdraws through its own elasticity. ”

“ 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. ”

“ The orbicularis oculi muscle, which is principally supplied by the portio-dura nerve, is paralyzed, though it still retains a partial power of contraction, owing to the anatomical fact that some terminal twigs of the third or motor pair of nerves of the orbit branch into this muscle.
The facial artery, V, and the facial vein, U, Plate 4, are in close connexion with the submaxillary gland. Oftentimes they traverse the substance of it. The lingual nerve and artery lie in some part of their course immediately beneath the gland. ”

“ There is a leash of four muscles rising from a spot behind the exit of the optic nerve from the cranium to the upper, under, anterior, and posterior sides of the eyeball. These are the superior, inferior, anterior, and posterior recti. Running from the front of the orbit obliquely to the underside of the eyeball is the inferior oblique muscle. Corresponding to it above is a superior oblique. A lachrymal gland lies in the postero-inferior angle of the orbit, and a Handerian gland in the corresponding position in front. ”

“ The muscle is well supplied with blood, and the nerve which endows it with energy is particularly well prevented from being compressed during the movements of the muscles amongst which it runs, any compression being very injurious. The upper edge of the blade-bone is notched, and a dense tissue or ligament stretches from one point of the notch to the opposite one, enclosing a small open space; now the nerve runs through this space, and is protected by the hard tissues of bone and ligament from the contraction of the soft muscles. ”

“ In Scorpio, according to Miss Beck, the dorso-ventral prosomatic muscles are situated near the middle line on each side and form the following well-marked series of pairs of muscles, shown in Fig. 110, A, taken from her paper, and thus described by her:—
1. The dorso-cheliceral-sternal muscle (61) is the most anterior of the dorso-ventral muscles. It is very small, and is attached to the carapace near the median line anteriorly to the central eyes.
2. The median dorso-preoral-entosclerite muscle (62) is a large muscle, between which and its fellow of the opposite side the eyes are situated. ”

“ It remains to be determined how many specimens need to be studied in order to obtain a fairly accurate picture of variation.
Comparison with Other Studies of Innervation
I accept the following concept of muscle-nerve relationship. All muscles of the pelvic limb of birds have developed phylogenetically [Pg 453] from either the dorsal extensor muscle mass or the ventral flexor muscle mass. The former was (at least originally) supplied by only the femoral and peroneal nerves ("dorsal" nerves) , the latter by only the obturator and tibial nerves ("ventral" nerves) . ”

“ In miners, who work for long periods lying on the side, the muscle may be paralysed by direct pressure on the terminal filaments of the nerve, and the nerve may also be involved as a result of disease in the sub-deltoid bursa.
The deltoid is wasted, and the acromion unduly prominent. In recent cases paralysis of the muscle is easily detected. In cases of long standing it is not so simple, because other muscles, the spinati, the clavicular fibres of the pectoral and the serratus, take its place and elevate the arm; there is always loss of sensation on the lateral aspect of the shoulder. ”

“ As previously explained, after a duction test of each of the four muscles of the right eye, the rotary prism before that eye should be placed out of position and the procedure for adduction, abduction, superduction and subduction repeated by means of the rotary prism before the left eye. In case of an existing imbalance, after testing the muscle of both right and left eyes, the refractionist can quickly determine which muscle or muscles may be lacking in strength (Fig. 24) . ”

“ The first branch, sometimes large, sometimes small, passes to the lymphatic gland in the hollow of the shoulder, and to the adjacent muscles; it supplies the clavotrapezius, acromiotrapezius, levator scapulæ ventralis, splenius, occipitoscapularis, and rhomboideus. A second branch passes between the subscapularis and supraspinatus muscles, dividing into various branches which supply the muscles named. The third branch pierces the supraspinatus muscle, just craniad of the acromion process, and ramifies in that muscle. ”

“ Whenever abroad muscle arises and terminates on one of the great cavities, it preserves everywhere nearly its breadth, because it has a large surface for its insertion. But if from a cavity it goes to a long bone, or to a small apophysis, then its fibres gradually approximate; it loses its breadth, increases in thickness, and terminates in an angle which is succeeded by a tendon, which concentrates into a very small space fibres widely scattered on the side of the cavity. ”

“ 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. ”

“ Furthermore, they have no striations, and their connection with the nerve fibers is less marked. They are also much smaller than the striated cells, being less than one one-hundredth of an inch in length and one three-thousandth of an inch in diameter.
In the formation of the non-striated muscles, the cells are attached to one another by a kind of muscle cement to form thin sheets or slender bundles. These differ from the striated muscles in several particulars. They are of a pale, whitish color, and they have no tendons. ”

“ It is interesting to notice that certain muscles are always exempt from paralysis. With the exception of a single case of paralysis of one temporal muscle, cited by Seguin,22 the muscles of the head, eyeballs, ears, larynx, and pharynx are always exempt, as are also the diaphragm and intercostals. The arrest of the spinal lesion below the medulla explains the immunity of muscles supplied by the vagus and spinal accessory nerves. But since the cervical plexus is often involved, the constant escape of the diaphragm, innervated by the phrenic nerve which comes from this plexus, is remarkable. ”

“ The eyeballs are generally turned upward and inward. The muscles are completely relaxed. The tendinous reflexes are exaggerated; pressure over a muscle or upon a nerve arouses a peculiar contraction of synergic muscles and of groups of muscles which are supplied by the excited nerve-trunk. The facial muscles, however, do not thus become contractured: they merely contract during the application of the stimulus. ”

“ Thus both layers of the muscle plate are concerned in forming the great longitudinal lateral muscles, though the splanchnic layer is converted into muscles very much sooner than the somatic [245] .
Each muscle-plate is at first a continuous structure, extending from the dorsal to the ventral surface, but after a time it becomes divided by a layer of connective tissue, which becomes developed nearly on a level with the lateral line, into a dorso-lateral and a ventro-lateral section. The ends of the muscle-plates continue for a long time to be formed of undifferentiated columnar cells. ”

“ This gives the muscle greater play than in us, and enables it to lift, more slowly perhaps, but more efficiently, for the arm-bone between the joint and the place where the muscle is attached, is the long arm of a lever which is shorter in man. Below the globular head of the arm-bone is the shaft or cylindrical part of the bone which gives origin to the three-headed muscle called triceps, and is covered by the two-headed one (biceps) already mentioned, besides the deltoid. ”