The clavipectoral fascia is a sheet of membrane filling in the space between clavicle and pectoralis minor, limited laterally by the coracoid process and passing medially to fuse with the external intercostal membrane of the upper two spaces. It splits above to enclose subclavius, being attached to the anterior and posterior ridges which limit the subclavian groove on the under surface of the clavicle. These two layers reappear above the clavicle as the lower attachment of the investing layer of deep cervical fascia, but there is no physical continuity between them, each fascia being firmly attached to the clavicle above and below, not passing over the bone.
At the lower border of subclavius the two layers fuse and may form a well-developed band, the costocoracoid ligament, stretching from the knuckle of the coracoid to the first costochondral junction. From this ligament the fascia stretches as a loosely felted membrane to the upper border of pectoralis minor, which muscle is enclosed by the splitting of the membrane into anterior and posterior leaves. These leaves are very thin and amount to little more than the epimysium of the muscle. They rejoin below pectoralis minor to extend downwards as the suspensory ligament of the axilla. The latter is attached to the axillary fascia over the floor of the axilla, and by its tension maintains the axillary hollow. The clavipectoral fascia is almost covered by pectoralis major and the anterior fibers of the deltoid, but a small extent appears in the infraclavicular fossa in the interval between these two muscles. In this situation it is pierced by four structures, two passing inwards, and two passing outwards. Passing inwards are lymphatics from the infraclavicular nodes to the apical nodes of the axilla, and the cephalic vein; passing outwards are the thoracoacromial vessels and the lateral pectoral nerve. The thoracoacromial artery has four main branches of distribution: clavicular, humeral, acromial and pectoral. These frequently pierce the fascia separately; their corresponding veins, however, join the cephalic vein anterior to the fascia. This is a characteristic arrangement in anatomy (compare, for example, with branches of the femoral artery below the groin, piercing the fascia lata separately from the veins which joint the great saphenous vein before the latter pierces the cribriform fascia.