While the muscles above enumerated comprise all those directly attached to the shoulder-girdle and trunk, they are of course assisted to some extent by the muscles forming the axillary folds, viz., the pectoralis major anteriorly and the latissimus dorsi and teres major posteriorly.

The shoulder-girdle is elevated by the upper fibres of the trapezius, levator scapulae, rhomboidei, sternomastoid (clavicular origin), and omohyoid. It is depressed by the lower fibres of the trapezius, latissimus dorsi, lower fibres of the serratus anterior (magnus), pectoralis major, pectoralis minor, and subclavius. It is drawn forward by the pectoralis major, minor, subclavius, serratus anterior, omohyoid, and, if the arm is fixed, by the teres major muscles. It is drawn back by the trapezius, rhomboidei, and latissimus dorsi muscles. Circumduction is effected by a combined action of various parts of these muscles.

Surface Anatomy

On observing the region of the shoulder it is noticed that it projects well out from the trunk, so that the arm hangs free. It has as its framework three bones - the clavicle and scapula above, forming the shoulder-girdle, and the humerus below. They radiate from the region of the joint, the clavicle toward the front, the scapula toward the back, and the humerus downward, forming the basis of the shape of the shoulder, which is modified by the muscles, fat, and skin.

The skin and fat bridge over and tend to obliterate the hollows and to a less extent obscure the prominences. This is more the case as applied to the muscles than the bones, hence the bones form the better landmarks or guides.

Age and sex modify the surface appearances. In children the bones are but slightly developed and their prominences not marked. Fat is usually abundant and it is often no easy task to recognize by the sense of touch the various anatomical parts and determine whether or not they have been injured. For this reason one should endeavor to increase his skill by taking advantage of every opportunity that offers for examination. In the case of women the same thing usually exists, but to a less degree. In the somewhat emaciated adult male the structures can be recognized to best advantage.

The clavicle is subcutaneous, and even in children and fat people can be felt throughout its entire length. Its large, knob-like inner extremity projects considerably above the upper edge of the sternum, which can be felt at the suprasternal notch. Take particular notice of its size and compare it with the one on the opposite side so as not to be misled as to its being diseased or luxated. Follow the bone to its outer extremity, which is higher than the inner, more so when lying down than when standing. A prominent ridge marks its outer extremity; if it is difficult to recognize, as will often be the case, then continue directly outward to the point of the shoulder, which is formed by the tip of the acromion process. Having recognized this point, the end of the clavicle will be found about 2.5 to 3 cm. (1 to 1 1/4 in.) directly inward from it.

Fig. 241.   Surface anatomy of the shoulder.

Fig. 241. - Surface anatomy of the shoulder.

In the median line above the sternum is the suprasternal notch with the prominent sternal origins of the sternomastoid muscles on each side. Just to the outer edge of these tendons lie the sternoclavicular joints. The one on the right side marks the ending of the innominate artery and the commencement of the right common carotid and subclavian. That on the left marks the left carotid with the subclavian directly to its outer side and a little posteriorly.

If the head is extended and turned to the opposite side the clavicular origin of the sternomastoid is made visible. It arises from the inner third of the bone.

The inner two-thirds of the clavicle is convex forward. Above this portion is the subclavian triangle in the supraclavicular fossa. The outer third of the clavicle is convex backward and from its upper surface the trapezius muscle can be felt proceeding upward. This leaves the middle third of the bone free from muscle.

Under the middle of the bone passes the subclavian artery. It curves upward about 2.5 cm. (1 in.) above the clavicle to descend again to the sternoclavicular joint. The arch so formed indicates the apex of the lung because the subclavian artery-rests on the pleura. The internal jugular vein passes down opposite the interval between the sternal and clavicular heads of the sternomastoid muscle.

Just above the clavicle, a little internal to its middle, and behind the clavicular origin of the sternomastoid muscle is seen the external jugular vein. It terminates in the subclavian vein, which lies to the inner (anterior) side of the artery. To the outer side of the artery the cords of the brachial plexus pass upward and inward. They become prominent in emaciated subjects when the head is turned forcibly toward the opposite side. The posterior belly of the omohyoid muscle varies much in its position, sometimes it lies behind the clavicle, at others two or three centimetres above it.

Immediately below the clavicle is the infraclavicular fossa. At its inner extremity can be felt the first rib. As it is exceedingly easy to mistake the ribs, it is best, in counting them, to locate the second rib by recognizing the angle of the sternum, (angle of Ludwig) to which it is opposite, on the surface of the sternum about 5 cm. (2 in.) below its upper edge. Attached to the lower edge of the inner half of the clavicle is the pectoralis major muscle and to the outer third the deltoid muscle.

This leaves one sixth of the lower edge of the clavicle free from muscular attachments. This forms the base of the subclavicular triangle and its two sides are formed by the adjacent edges of the pectoralis major and deltoid muscles. Beneath this triangle runs the first portion of the axillary artery with the vein to its inner side and the cords of the brachial plexus to its outer side. Deep pressure at this point can compress it against the second rib, but not so effectively as above the clavicle.

Just to the outer side of the junction of the middle and outer thirds of the clavicle, in front of the deepest part of the concavity of the clavicle and about 2.5 cm. (1 in.) below it, is the coracoid process. It is better felt by pressing the fingers flat on the surface than by digging them in. It is somewhat obscured by the edge of the deltoid muscle, which covers it. Running from the coracoid to the acromion process is the sharp edge of the coraco-acromial ligament. An incision midway between the two processes would open the joint and strike the long biceps tendon as it winds over the head of the humerus to reach the upper edge of the glenoid cavity.

Beneath the acromion process is felt the greater tuberosity of the humerus. If the arm is placed alongside of the body with the palm facing forward, a distinct groove can be felt to the inner side of the acromion process passing downward on a line with the middle of the arm. It is the bicipital groove for the long tendon of the biceps muscle. The bony process of the humerus to its outer side is the greater tuberosity and that to its inner side, between it and the coracoid process, on a slightly 1ower level, is the lesser tuberosity. It will be noted that the greater tuberosity projects beyond the acromion process and forms the prominence of the shoulder. On rotating the arm the tuberosities can be distinctly felt moving under the deltoid muscle.

Following the acromion process around toward the back it turns abruptly where it joins the spine of the scapula, forming a distinct angle. This angle is quite prominent, can be readily seen and felt, and can be used as a landmark for measuring the length of the humerus. If the spine of the scapula is followed still farther it ends in its root at the posterior border of the bone opposite the upper edge of the fourth rib and third thoracic spine. This marks the upper extremity of the fissure of the lung; with the arm to the side, the lower angle of the scapula lies over the seventh interspace.