The muscles of the upper limb are divisible into the following groups
I. Muscles connecting the upper limb with the vertebral column.
II. Muscles connecting the upper limb with the anterior and lateral thoracic walls.
III. Muscles of the shoulder.
IV. Muscles of the upper arm.
V. Muscles of the forearm.
VI. Muscles of the hand.
I. THE MUSCLES CONNECTING THE UPPER LIMB WITH THE VERTEBRAL COLUMN
|Latissimus dorsi||Rhomboideus minor|
The superficial fascia of the back forms a layer of considerable thickness and strength; and contains a quantity of granular fat. It is continuous with the general superficial fascia.
The deep fascia is a dense fibrous layer, attached above to the superior nuchal line of the occipital bone; in the median plane it is fixed to the ligamentum nuchae and supraspinous ligament, and to the spines of all the vertebrae below the seventh cervical; laterally, in. the neck it is continuous with the deep cervical fascia; over the shoulder it is attached to the spine and acromion of the scapula, and is continued downwards over the Deltoid to the arm; on the thorax it is continuous with the deep fascia of the axilla and chest, and on the abdomen with that covering the abdominal muscles; below, it is attached to the crest of the ilium.
The Trapezius (fig. 618) is a flat, triangular muscle, covering the back of the neck and shoulder. It arises from the medial one-third of the superior nuchal line of the occipital bone, the external occipital protuberance, the ligamentum nuchae, the spine of the seventh cervical, and the spines of all the thoracic vertebrae, and the corresponding portion of the supraspinous ligament. The superior fibers proceed downwards and laterally, the inferior upwards and laterally, and the middle horizontally, the superior fibers are inserted into the posterior border of the lateral one-third of the clavicle; the middle fibers into the medial margin of the acromion and the superior lip of the crest of the spine of the scapula; the inferior fibers converge and end in an aponeurosis, which glides over the smooth triangular surface at the medial end of the spine of the scapula and is inserted into a tubercle at the apex of this smooth triangular surface. The upper part of the Trapezius is connected to the occipital bone by a thin fibrous lamina, firmly adherent to the skin; the middle part arises by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebra; the lower part arises by short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or quadrangle; two angles corresponding to the shoulders; a third to the occipital protuberance and the fourth to the spine of the twelfth thoracic vertebra.
The clavicular insertion of this muscle varies in extent : it sometimes reaches as far as the middle of the clavicle, and occasionally blends with the posterior edge of the Sternocleidomastoid.
The two muscles cover the back of the neck and shoulders like a monk’s cowl and therefore the Trapezius is sometimes termed the Musculus cucullaria.
Nerve-supply.-The Trapezius is supplied by the accessory nerve and by branches from the third and fourth. cervical nerves.
Actions.-When the head is fixed, the Trapezius acting with the Levator scapulae elevates the scapula and with it the point of the shoulder; acting with the Serratus anterior, the Trapezius rotates the scapula in a forward direction so that the arm can be raised above the head; acting with the Rhomboids, the Trapezius retracts the scapula, and so braces back the shoulder. When the shoulder is fixed, the Trapezius draws the bead backwards and laterally.
The Latissimus dorsi (fig. 618) is a large, triangular, flat muscle, which covers the lumbar region and the lower one-half of the thoracic region; but its fibers converge to a narrow tendon of insertion. It arises by tendinous fibers from the spines of the lower six thoracic vertebra under. cover of the Trapezius, and from the posterior layer of the lumbar fascia (p. 534), by which it is attached to the spines of the lumbar and sacral vertebrae, to the supraspinous ligament, and to the posterior part of the crest of the ilium, In addition, it arises by- muscular fibers from the posterior part of the outer lip of the crest of the ilium, lateral to the margin of the Sacrospinalis, and from the three or four lower ribs by fleshy digitations which are interposed between similar processes of the Obliquus abdominis externus (fig. 600). From this extensive origin the fibers pass in different directions, the upper ones horizontally, the middle obliquely upwards, and the lower almost vertically upwards, so as to converge and form a thick fasciculus, the upper part of which crosses, and usually receives a few fibers from, the inferior angle of the scapula. The muscle curves around the lower border of the Teres major, and is twisted upon itself, so that the superior fibers become at first posterior and then inferior, and the ascending fibers at first anterior and then superior. It ends in a quadrilateral tendon, about 7 cm. long, which passes in front of the tendon of the Teres major, and is inserted into the bottom of the bicipital groove (intertubercular sulcus) of the humerus, giving an expansion to the deep fascia of the upper arm; its insertion extends higher on the humerus than that of the tendon of the Pectoralis major. The lower border of its tendon is united with that of the Teres major, the surfaces of the two tendons being separated near their insertions by a bursa; another bursa is sometimes interposed between the muscle and the inferior angle of the scapula.
A muscular slip, named the axillary arch, varying from 7 to 10 cm in length, and from 5 to 15 mm in breadth, occasionally springs from the upper edge of the Latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the pectoralis major, the Coracobrachialis, or the fascia over the Biceps. This axillary arch crosses the axillary artery, just above the spot usually selected for the application of a ligature, and may mislead the surgeon during the operation. It is present in about seven per cent of subjects and may be easily recognized by the direction of its fibers.
A fibrous slip usually passes from the lower border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the Triceps. This is occasionally muscular, and is the representative of the dorso-epitrochlearis brachii of apes.
Nerve-supply.-The nerve to Latissimus dorsi (thoracodorsal nerve) is derived from the posterior cord of the brachial plexus (C. 6, 7 and 8).
Actions.-The Latissimus dorsi depresses the humerus, draws it backwards, and rotates it medially. It takes part in violent expiratory efforts, such as coughing. When both arms are fixed it helps to pull the trunk upwards and forwards as in climbing.
The lower part of the lateral margin of the Latissimus dorsi is separated from the posterior free border of the External oblique muscle by a small triangular interval, named the lumbar triangle, the base of which is formed by the iliac crest, and the floor by the Internal oblique muscle (fig. 618). Another triangle, sometimes termed the triangle of auscultation, is situated behind the scapula. It is bounded above by the Trapezius, below by the Latissimus dorsi, and laterally by the medial border of the scapula; the floor is partly formed by the Rhomboideus major. If the scapula be drawn forwards by folding the arms across the chest, and the trunk bent forwards, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation of the lung.
The Rhomboideus minor (fig. 618) arises from the lower part of the ligamentum nuchae and from the spines of the seventh cervical and first thoracic vertebrae; it is inserted into the base of the triangular smooth surface at the apex of the spine of the scapula. It is usually separated from the Rhomboideus major by a slight interval, but the adjacent margins of the two muscles are occasionally united.
Nerve-supply.-The nerve to the Rhomboid muscles arises from the anterior primary ramus of the fifth cervical nerve in the substance of the Scalenus medius muscle.
Action.-The Rhomboid muscles, acting with the Trapezius, retract the scapula and brace back the shoulder; acting with the Levator scapulae and Pectoralis minor, they rotate the scapula backwards and so depress the point. of the shoulder.
The Levator scapulae (figs. 593, 618) is situated at the back and side of the neck. It arises by tendinous slips from the transverse processes of the atlas and axis and from the posterior tubercles of the transverse processes of the third and fourth cervical vertebrae. It is inserted into the medial border of the scapula, between the superior angle and the triangular smooth surface at the apex of the spine.
Nerve-supply.-The Levator scapulae is supplied directly by branches from the third and fourth cervical nerves, and by a, branch from the nerve to the Rhomboids (C. 5).
Actions.—If the cervical part of the vertebral column be fixed, the Levator scapula; may act with the Trapezius to elevate the scapula, or to sustain a weight carried on the shoulder; or it may act with the Rhomboids and Pectoralis minor to rotate the scapula backwards and so depress the point of the shoulder. If the shoulder is fixed, the muscle inclines the neck to the same side.
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