The following features of the pectoral region can be seen or felt on the surface of body.
1. The clavicle lies horizontally at the root of the neck, separating it from the front of the chest. The bone is subcutaneous, and therefore, palpable, throughout its length. It is convex forwards in its medial two-thirds, and concave forwards in its lateral one-third.
Medially, it articulates with the sternum at the sternoclavicular joint, and laterally with the acromion at the acromioclavicular joint. Both the joints are palpable because of the upward projecting ends of the clavicle. The sternoclavicular joint may be masked by the sternocleidomastoid muscle.
2. The jugular notch (interclavicular or suprasternal notch) lies between the medial ends of the clavicles, at the superior border of the manubrium sterni.
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3. The sternal angle (angle of Louis) is felt as a transverse ridge about 5 cm below the jugular notch. It marks the manubriosternal joint. Laterally, on either side, the second costal cartilage joins the sternum at this level.
The sternal angle thus serves as a landmark for identification of the second rib. Other ribs can be identified by counting downwards from the second rib.
4. The epigastric fossa (pit of the stomach) is the depression in the infrasternal angle. The fossa overlies the xiphoid process, and is bounded on each side by the seventh costal cartilage.
5. The nipple is markedly variable in position in females. In males, and in immature females, it usually lies in the fourth intercostal space just medial to the midclavicular line; or 10 cm from the midsternal line. In fact, the position of the nipple is variable even in males.
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6. The midclavicular line passes vertically through the tip of the ninth costal cartilage and the midinguinal point.
7. The infraclavicular fossa (deltopectoral triangle) is a triangular depression below the junction of the lateral and middle thirds of the clavicle. It is bounded medially by the pectoralis major, laterally by the anterior fibres of the deltoid, and superiorly by the clavicle.
8. The tip of the coracoid process of the scapula lies 2-3 cm below the clavicle, overlapped by the anterior fibres of the deltoid. It can be felt on deep palpation just lateral to the infraclavicular fossa.
9. The acromion of the scapula (acron = summit; omos = shoulder) is a flattened piece of bone that lies subcutaneously forming the top of the shoulder. The posterior end of its lateral border is called the acromial angle, where it is continuous with the lower lip of the crest of the spine of the scapula.
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The anterior end of its medial border articulates with the clavicle at the acromioclavicular joint. The joint can be felt because the clavicle projects slightly above the acromion.
10. The deltoid is triangular muscle with its apex directed downwards. It forms the rounded contour of the shoulder, extending vertically from the acromion to the deltoid tuberosity of the humerus.
11. The axilla (or armpit) is a pyramidal space between the arm and chest. When the arm is raised (abducted) the floor of the axilla rises, the anterior and posterior folds stand out, and the space becomes more prominent.
The anterior axillary fold contains the lower border of the pectoralis major, and posterior axillary fold contains the tendon of the latissimus dorsi winding round the fleshy teres major.
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The medial wall of the axilla is formed by the upper 4 ribs covered by the serratus anterior. The narrow lateral wall presents the upper part of the humerus covered by the short head of the biceps, and the coracobrachialis.
Axillary arterial pulsations can be felt by pressing the artery against the humerus. The cords of the brachial plexus can also be rolled against the humerus. The head of the humerus can be felt by pressing the fingers upwards into the axilla.
12. The midaxillary line is a vertical line drawn midway between the anterior and posterior axillary folds.