Superficial Fascia.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.
Deep Fascia.The deep fascia is a dense fibrous layer, attached above to the superior nuchal line of the occipital bone; in the middle line it is attached to the ligamentum nuchæ and supraspinal ligament, and to the spinous processes of all the vertebræ 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 of the scapula and to the acromion, and is continued downward over the Deltoideus 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. 409) is a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protuberance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nuchæ, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebræ, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibers proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibers are inserted into the posterior border of the lateral third of the clavicle; the middle fibers into the medial margin of the acromion, and into the superior lip of the posterior border of the spine of the scapula; the inferior fibers converge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebræ, and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corresponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra.
Variations.The attachments to the dorsal vertebræ are often reduced and the lower ones are often wanting; the occipital attachment is often wanting; separation between cervical and dorsal portions is frequent. Extensive deficiencies and complete absence occur.
FIG. 409 Muscles connecting the upper extremity to the vertebral column. (See enlarged image)
The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it.
The Latissimus dorsi(Fig. 409) is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region, and is gradually contracted into a narrow fasciculus at its insertion into the humerus. It arises by tendinous fibers from the spinous processes of the lower six thoracic vertebræ and from the posterior layer of the lumbodorsal fascia (see page 397), by which it is attached to the spines of the lumbar and sacral vertebræ, to the supraspinal ligament, and to the posterior part of the crest of the ilium. It also arises by muscular fibers from the external 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. 392, page 409). From this extensive origin the fibers pass in different directions, the upper ones horizontally, the middle obliquely upward, and the lower vertically upward, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and usually receives a few fibers from it. 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 vertical 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 intertubercular groove of the humerus; 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 being separated near their insertions by a bursa; another bursa is sometimes interposed between the muscle and the inferior angle of the scapula. The tendon of the muscle gives off an expansion to the deep fascia of the arm.
A muscular slip, 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 brachii. 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 7 per cent. of subjects and may be easily recognized by the transverse 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 brachii. This is occasionally muscular, and is the representative of the Dorsoepitrochlearis brachii of apes.
The lateral margin of the Latissimus dorsi is separated below from the Obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the Obliquus internus abdominis. Another triangle is situated behind the scapula. It is bounded above by the Trapezius, below by the Latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the Rhomboideus major. If the scapula be drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for ausculation. The space is therefore known as the triangle of ausculation.
Nerves.The Trapezius is supplied by the accessory nerve, and by branches from the third and fourth cervical nerves; the Latissimus dorsi by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve.
The Rhomboideus major(Fig. 409)arises by tendinous fibers from the spinous processes of the second, third, fourth, and fifth thoracic vertebræ and the supraspinal ligament, and is inserted into a narrow tendinous arch, attached above to the lower part of the triangular surface at the root of the spine of the scapula; below to the inferior angle, the arch being connected to the vertebral border by a thin membrane. When the arch extends, as it occasionally does, only a short distance, the muscular fibers are inserted directly into the scapula.
The Rhomboideus minor(Fig. 409) arises from the lower part of the ligamentum nuchæ and from the spinous processes of the seventh cervical and first thoracic vertebræ. It is inserted into the base of the triangular smooth surface at the root of the spine of the scapula, and is usually separated from the Rhomboideus major by a slight interval, but the adjacent margins of the two muscles are occasionally united.
Variations.The vertebral and scapular attachments of the two muscles vary in extent. A small slip from the scapula to the occipital bone close to the minor occasionally occurs, the Rhomboideus occipitalis muscle.
The Levator scapulæ. (Levator anguli scapulæ) (Fig. 409) 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 vertebræ. It is inserted into the vertebral border of the scapula, between the medial angle and the triangular smooth surface at the root of the spine.
Variations.The number of vertebral attachments varies; a slip may extend to the occipital or mastoid, to the Trapezius, Scalene or Serratus anterior, or to the first or second rib. The muscle may be subdivided into several distinct parts from origin to insertion. Levator claviculæ from the transverse processes of one or two upper cervical vertebræ to the outer end of the clavicle corresponds to a muscle of lower animals. More or less union with the Serratus anterior.
Nerves.The Rhomboidei are supplied by the dorsal scapular nerve from the fifth cervical; the Levator scapulæ by the third and fourth cervical nerves, and frequently by a branch from the dorsal scapular.
Actions.The movements effected by the preceding muscles are numerous, as may be conceived from their extensive attachments. When the whole Trapezius is in action it retracts the scapula and braces back the shoulder; if the head be fixed, the upper part of the muscle will elevate the point of the shoulder, as in supporting weights; when the lower fibers contract they assist in depressing the scapula. The middle and lower fibers of the muscle rotate the scapula, causing elevation of the acromion. If the shoulders be fixed, the Trapezii, acting together, will draw the head directly backward; or if only one act, the head is drawn to the corresponding side.
When the Latissimus dorsi acts upon the humerus, it depresses and draws it backward, and at the same time rotates it inward. It is the muscle which is principally employed in giving a downward blow, as in felling a tree or in sabre practice. If the arm be fixed, the muscle may act in various ways upon the trunk; thus, it may raise the lower ribs and assist in forcible inspiration; or, if both arms be fixed, the two muscles may assist the abdominal muscles and Pectorales in suspending and drawing the trunk forward, as in climbing.
If the head be fixed, the Levator scapulæ raises the medial angle of the scapula; if the shoulder be fixed, the muscle inclines the neck to the corresponding side and rotates it in the same direction. The Rhomboidei carry the inferior angle backward and upward, thus producing a slight rotation of the scapula upon the side of the chest, the Rhomboideus major acting especially on the inferior angle of the scapula, through the tendinous arch by which it is inserted. The Rhomboidei, acting together with the middle and inferior fibers of the Trapezius, will retract the scapula.