Pectoralis muscle

“ The pectoralis major rises from the inner half of the clavicle, the front of the sternum, and the cartilages of the true ribs and its fibers converge to form a fan-shaped muscle, which is inserted by a flat tendon into the edge of the bicipital groove on the humerus. It draws the arm forward and inward and helps considerably in forced inspiration. The serratus magnus rises from the outer surface and upper border of the eight upper ribs and from an aponeurosis covering the upper intercostal spaces, and is inserted along the whole length of the posterior border of the scapula. ”

“ Muscles of the Thorax. A. Breast-muscles (connecting the arm and thorax) (Fig. 65, page 109) .
The muscles connecting the arm with the sternum, corresponding to the pectoralis muscles of man, fall into a considerable [145] number of not always clearly separated bundles in the cat. We shall distinguish by name four such bundles; these might be, and frequently are, further subdivided.
M. pectoantibrachialis (Fig. 65, m) .—This is a small flat bundle about one or two centimeters wide, forming the most superficial portion of the pectoralis group.
Origin on the lateral surface of the manubrium. ”

“ The chest is supplied with numerous muscles which move the ribs up and down in the act of breathing. A great, fan-shaped muscle, called the pectoralis major, lies on the chest. It extends from the chest to the arm and helps draw the arm inward and forward. The arm is raised from the side by a large triangular muscle on the shoulder, the deltoid, so called from its resemblance to the Greek letter delta, Δ. The biceps, or two-headed muscle, forms a large part of the fleshy mass in front of the arm. ”

“ The subclavius muscle, E, like the pronator quadratus muscle of the forearm, serves rather to further the displacement of the broken ends of the bone than to hold them in situ.
If the head of the humerus be dislocated forwards beneath L, Plate 11, the coracoid attachment of the pectoralis minor muscle, it must press out of their proper place and put tensely upon the stretch the axillary vessels and plexus of nerves. ”

“ Operation by two flaps, external and internal.—The outer—beginning nearly an inch below the acromion process, the hair in the axilla having been previously removed—is to be carried down with a gentle curve so deeply as to divide the deltoid muscle, and to show the long head of the triceps at its under and outer edge. The second incision is to be carried in a similar direction on the inside, through the deltoid muscle, but need not divide the insertion of the pectoralis major, which should be exposed. ”

“ In woman it is generally less curved, smoother, and more slender than in man, and as bone is rough when the muscles attached are powerful, the right clavicle, being used more, is generally rougher and thicker than the left. Among the muscles attached are the large neck muscle, the sterno-cleido-mastoid, whose tendons form the presternal notch, the trapezius, the pectoralis major, and the deltoid. ”

“ The legs were normal. The electrical irritability of the left arm was only slightly diminished. There was a well-marked hypertrichosis of the left forearm, the skin of which was slightly purple and discolored. The patient himself made an attempt to burn his arm with a lighted cigar, to see if he could feel the pain. He showed the scar but had felt nothing. The pectoralis major muscle did not contract. If the left arm was started actively swinging, it kept on swinging inertly. The left hand showed hyperidrosis. The small hand muscles were emaciated but electrically normal. ”

“ In the pectoral, which has never been found hypertrophied, the wasting process always sets in the earliest, and advances to the greatest extent. The pectoral muscle is thus the exact antithesis of the gastrocnemius, while the deltoid more nearly resembles [p. 566] the gastrocnemius than any other muscle of the upper extremity. After the pectoral the latissimus dorsi, then the trapezius scapular muscles (including the serratus magnus) , those of the arm and fore arm, the muscles of the neck, are found more or less wasted by the time the disease is fully developed. ”

“ We will recall at the outset that the lesser pectoral muscle in man is completely covered by the great. In animals this is not the case; the lesser pectoral being very highly developed, projects beyond the great pectoral posteriorly, and occupies to a greater or less extent the inferior surface of the abdomen.
It also consists of two parts: one anterior, which we designate by the name of sterno-prescapular; the other, posterior, bearing that of sterno-humeral. ”

“ Luxation of the Shoulder-joint is prevented, by the arrangement and structure of the parts, from taking place in any direction ex593cepting towards the axilla—downwards into the hollow of the armpit, downwards and forwards under the lower border of the pectoral muscle. Occasionally, though very rarely indeed, displacement occurs backwards. On the anterior and inferior aspects, the articulation is not supported, as at its other sides, either by muscular substance or by processes of bone. ”

“ The great pectoral muscle of one side is separated from that of the opposite side along the median line, and especially above and in front, by a groove which is more or less deep, according as the muscles are more or less developed. ”

“ To proceed to the reduction of a luxation of the humerus, it is necessary to have such a number of assistants as to be able, according to the resistance of the parts, to increase the force intended to overcome it. But two are commonly sufficient. They should furnish themselves with a linen ball, thick enough to project beyond the level of the pectoralis major and the latissimus dorsi, when placed in the axilla, and two straps, one formed of flannel doubled several times, four inches broad, and eight or nine feet long, the other of a napkin regularly folded. ”

“ Muscular action is one permanent cause of a new displacement. Suppose the humerus luxated downward, the pectoralis major, and the deltoid muscles draw its superior extremity upward and inward, which, offering to their action but a feeble resistance, changes its position and that in a two-fold direction.
27. The different motions of the arm may also, according to their direction, produce the same effect. Thus we have often witnessed a luxation inwards succeeding to a luxation downwards, in consequence of unskilful attempts to reduce it. ”

“ All muscles are not of this form—sometimes they are strap-shaped; and not all of them end in tendons. As the most important act of the bird’s life that depends upon its muscles is flying, it is not surprising to find that the muscle which effects the downward stroke of the wing is the largest. This muscle is known as the great pectoral, and it is said to be almost as large as all the other muscles of the body put together. The way in which a muscle effects the movements of the bones to which it is attached is by contracting. All muscles are able to contract ”

“ The mediad component would increase as the jaw approached full adduction. Neither is there anatomical evidence for an adductor arising from the quadrate wing of the pterygoid. The bone is smooth, hard, and without any marks that might be interpreted as muscle scars.
The internal adductor or pterygoid musculature in Captorhinus consisted of anterior and posterior components. The anterior pterygoid arose from the lateral edge and the dorsal surface of the pterygoid flange. ”

“ The pectoral and clavobrachial muscles have been cut and laid aside, their ends being shown; only a part of the nerves are exhibited. 1, M. clavobrachialis; 2, cut end of M. pectoralis major; 3, cut end of M. pectoralis minor; 4, M. biceps; 5, M. teres major; 6, M. epitrochlearis, partly cut and turned back; 7, M. latissimus dorsi, partly cut; 8, M. pectoralis minor; 9, M. pectoralis major; 10, short portion of caput mediale of M. triceps brachii. a, branches of the thyrocervical axis to clavobrachial and clavotrapezius muscles; b, suprascapular nerve; c, first subscapular nerve ”

“ The extensor muscle of the wing does not pull on the power arm, but on the resistant arm on the other side of the fulcrum (c) . The illustration shows, however, how such a case is possible. The membrane of the joint fastening the wing-stalk to the thorax is turned up outwards below the stalk like a pouch. The tendon of the flexor of the wing passes through this pouch to its point of attachment (c) lying on the other side of the fulcrum (d) . Thus it is very simply explained how two muscles which act in the same direction can nevertheless have an entirely contrary working power. ”

“ All the fibres of the voluntary muscles are straight, those of the sphincters excepted. They are either parallel as in the rhomboids, or obliquely situated in relation to each other, as in the great pectoral. Sometimes in the same muscle many sets cross each other in different directions, as we see in the masseter; but this crossing is wholly different from that of the involuntary muscles in which there is more crossing of fibres, whilst here we see only fasciculi in different directions, in juxta-position to each other. ”

“ 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 ”

“ 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. ”

“ And it is clear that the motive power of the pectoral muscles in men is much less than is necessary for flight, for in birds the bulk and weight of the muscles for flapping the wings are not less than a sixth part of the entire weight of the body. Therefore, it would be necessary that the pectoral muscles of a man should weigh more than a sixth part of the entire weight of his body ”

“ Apart from a function connected to the presence of skeletal elements, the specific morphology of frilled protractor muscles could also provide a stabilizing function as their lobes might prevent lateral shear of the main protractor muscle element. In addition, contraction and relaxation of the lobes could lead to a more rapid exchange of the coelomic fluid located at the fluid-tissue boundary along the muscle's surface. ”

“ 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. ”

“ In the muscles of animal life, when the contraction ceases, the muscle does not in general go back itself to the state it was in antecedent to the contraction, but it is drawn back to it by its antagonist; for example, when the biceps is contracted to bend the fore-arm and its contraction ceases, it becomes passive ”

“ The muscle retains its flat aspect until its insertion on the stereom at both ends (Fig. 3B, F) . The corresponding muscle scars reflect the flat aspect of the entire muscle (Fig. 3C, D, G, H) . Likewise, the frilled protractor muscle of E. mathaei inserts onto epiphysis (Fig. 3I) and perignathic girdle (Fig. 3M) . As the muscle maintains a frilled aspect throughout its entire length (Fig. 3J, N) , the muscle scars on epiphysis and perignathic girdle bear the imprint of the main muscle element as well as those of the individual, adaxially-facing lobes (Fig. 3K, L, O, P) . ”

“ The former develop particularly the chest, stretch the pectoral muscles, and lengthen the collar-bones. The latter increase the volume and power of the extensors of the shoulder, arm, and forearm, and are to be sedulously practised, because we have fewer common and daily movements of these muscles than of their antagonists, the flexors, and they are consequently weaker in most persons. The windows should be widely opened, and the room warmed by the sun alone. ”

“ The muscles of the Ecardines differ from those of the Testicardines inasmuch as they do not terminate in a tendon, but the muscle fibres run straight from shell to shell. They are also more numerous. In Crania there is an anterior and a posterior pair of occlusor muscles, and two pairs of oblique muscles, which seem when they contract together to move the dorsal shell forwards, or when they contract alternately to slightly rotate it. ”