This region may be divided into clavi pectoral, deltoid, and scapular portions. The clavi pectoral region is bounded by the clavicle above, the sternum internally, lower border of the pectoralis major below, and the groove between the pectoralis and deltoid externally. The skin is thin and freely movable, while the subcutaneous tissue, particularly in the female, is generally abundant. The clavicle forms a prominent landmark, the acromial end being generally the least prominent portion, while, when the acromio-clavicular ligaments are relaxed, it may be very prominent, simulating subluxation. While the axis of the clavicle is normally directed outwards and upwards, so that the sterno-clavicular articulation is in line with the head of the humerus, it may in weakly persons incline downwards at the outer end. The deltoid tubercle is a small bony projection, situated about the centre of the outer-curve, on the anterior border, which, if well developed, might be mistaken for an exostosis. A bursa frequently develops over the outer part of the clavicle in those who carry weights on the shoulder, and lipomas are sometimes met with in the same region. The infraclavicular fossa lies under the outer third of the clavicle, which bounds it above, and is directed downwards and outwards between the pectoralis major and deltoid. It overlies the upper part of the axilla, lodges the cephalic vein and a branch of the acromio-thoracic artery, and the axillary artery may be felt and compressed against the second rib by deep pressure in it. It is obliterated in subcoracoid dislocations of the humerus, some fractures of the clavicle, axillary swellings, and by superficial oedema. The coracoid process lies just to its outer side, covered by some fibres of the deltoid. When the arm hangs at the side with the palm directed forwards, the bicipital groove also looks forward, and lies midway between the acromial and coracoid processes. In this position also the acromion, external condyle, and styloid process of radius all lie in the same line. The lower border of the pectoralis major constitutes the anterior fold of the axilla. The line of the axillary artery, when the arm is raised from the side, runs frorn the centre of the clavicle to the inner side of the coraco-brachialis. The upper border of the pectoralis minor is indicated by a line from the costo-chondral junction of the third rib to the coracoid. The point of intersection of these two lines indicates the position of the acromio-thoracic artery. A line from the costo-chondral junction of the fifth rib to the coracoid indicates the lower border of the pectoralis minor, and the long thoracic artery which runs along that border.
The deltoid region corresponds to the deltoid muscle, being limited above by the outer third of the anterior border of the clavicle, tip and outer border of the acromion, and lower border of the spine of scapula. It extends almost to the centre of the humerus. The skin in this region is rather thick and coarse, and is bound to the fascia of the underlying muscles by fascial septa. The rounded contour of the shoulder depends on both the deltoid muscle and the tuberosities of the humerus. If the muscle be atrophied or the head of the bone displaced, the acromion process, which normally does not form a projection, stands out prominently, and the tip of the fingers may even be inserted beneath it. The junction of the acromion with the inferior border of the scapular spine is marked by the acromial angle, which is often the best marked portion of the acromion, and is used in taking various measurements. It is useful to remember in examining for dislocation that the internal condyle of the humerus indicates the direction of the articular surface of the head. The most prominent portion of the shoulder in front is formed by the great tuberosity. The coracoid process lies just to the outer side of the infraclavicular fossa, and is overlapped by the anterior border of the deltoid muscle. The posterior circumflex artery and circumflex nerve cross the humerus horizontally a finger's breadth above the centre of the vertical length of the deltoid.
The scapular region corresponds to the bone, which extends from the second to the seventh rib, and is divided by the spine into supra- and infraspinous regions. The skin in this region is thick, and closely adherent to the dense subcutaneous tissue, and is frequently the seat of 00ils and carbuncles. The scapular spine forms a prominent landmark, and its inner extremity is opposite the spine of the third dorsal vertebra. The vertebral border and spine of the scapula are easily palpated, while the anterior border is covered by the infraspinatus and teres muscles. The anterior surface of the scapula gives origin to the subscapularis, which forms the greater part of the posterior axillary wall. The latissimus dorsi forms the posterior fold of the axilla, and lies at a lower level than the pectoralis major, which forms the anterior fold, and lies at the level of the fifth rib.