24 THE SUPERIOR EXTREMITY 



on the lateral part of the pectoralis minor. Cut through the 

 sternocostal part of the pectoralis major about two inches from 

 the lateral border of the sternum. Turn the medial part towards 

 the median plane ; verify its attachment to the costal cartilages 

 and to the sternum and to the aponeurosis of the external oblique 

 muscle of the abdomen. Turn the lateral part of the muscle 

 towards the arm ; whilst doing that, secure the medial anterior 

 thoracic nerve, which perforates the pectoralis minor and ends 

 in the pectoralis major. Examine the insertion of the pectoralis 

 major. Note that the tendon of insertion consists of two laminae 

 which are united together below ; in other words, the tendon is 

 folded on itself ; and between the two laminae a mucous bursa 

 is frequently interposed. The clavicular fibres and the upper 

 sternocostal fibres are attached to the anterior lamina, the lower 

 sternocostal fibres to the posterior lamina. Both laminae are 

 attached to the lateral lip of the intertubercular sulcus of the 

 humerus, but the deep lamina ascends to a more proximal level, 

 and becomes continuous with a layer of fascia which is attached 

 to the lesser tubercle of the humerus. The inferior border of the 

 tendon of insertion is continuous with the deep fascia of the arm. 

 When the pectoralis major is completely reflected a continuous 

 sheet of fascia is exposed, which extends from the clavicle 

 superiorly to the axillary fascia inferiorly, and from the wall of 

 the thorax medially to the arm laterally ; the sheet of fascia is 

 the so-called clavipectoral fascia or suspensory ligament of the 

 axilla. It is because of the attachment of that fascial sheet to 

 the clavicle superiorly and to the axillary fascia inferiorly that 

 the floor of the axilla is raised as the arm is abducted from the 

 side and the clavicle is elevated. The pectoralis minor muscle, 

 passing obliquely from its origin on the thoracic wall to its 

 insertion into the coracoid process of the scapula, runs through 

 the substance of the clavipectoral fascia and divides it into three 

 parts : (i) the part above the muscle, (2) the part which encloses 

 the muscle, and (3) the part below the muscle. The uppermost 

 part is the costo-coracoid membrane, the intermediate part is the 

 sheath of the pectoralis minor. No special term is applied to 

 the lowest part, but it should be noted that it lies posterior to the 

 lower part of the pectoralis major, and that it covers the distal 

 portions of the axillary vessels and nerves. 



Membrana Costocoracoidea. The costo-coracoid mem- 

 brane occupies the gap between the clavicle and the pectoralis 

 minor. It extends from the first rib medially to the coracoid 

 process laterally, and from the clavicle above to the pectoralis 

 minor below. Its upper part is split into two layers, an 

 anterior and a posterior, which are attached to the corre- 

 sponding borders of the clavicle. Enclosed between them is 

 the subclavius muscle. The strongest part of the membrane 

 is that which extends along the lower border of the sub- 

 clavius, from the first rib to the coracoid process ; that portion 

 is frequently called the costo-coracoid ligament. The membrane 

 is continuous below with the fascial sheath of the pectoralis 



