378 THE MUSCLES AND FASCIA 



fascia on the axillary floor, and hence it is sometimes named the suspensory l><ia- 

 ment of the axilla. At the lower part of the thoracic region this fascia is well de- 

 veloped, and is continuous with the fibrous sheath of the Recti muscles. 



The Pectoralis major (Fig. 229) is a broad, thick, triangular muscle, situated 

 at the upper and fore part of the chest, in front of the axilla. It arises from the 

 anterior surface of the sternal half of the clavicle ; from half the breadth of the 

 anterior surface of the sternum, as low down as the attachment of the cartilage 

 of the sixth or seventh rib ; this portion of its origin consists of aponeurotic 

 fibres, which intersect with those of the opposite muscle ; it also arises from the 

 cartilages of all the true ribs, with the exception, frequently, of the first or of the 

 seventh, or both ; and from the aponeurosis of the External oblique muscle of the 

 abdomen. The fibres from this extensive origin converge toward its insertion, 

 giving to the muscle a radiated appearance. Those fibres which arise from the 

 clavicle pass obliquely outward and downward, and are usually separated from the 

 rest by a cellular interval : those from the lower part of the sternum, and the 

 cartilages of the lower true ribs, pass upward and outward, whilst the middle 

 fibres pass horizontally. They all terminate in a flat tendon, about two inches 

 broad, which is inserted into the outer bicipital ridge of the humerus. This 

 tendon consists of two laminae, placed one in front of the other, and usually 

 blended together below. The anterior, the thicker, receives the clavicular and 

 upper half of the sternal portion of the muscle ; and its fibres are inserted in the 

 same order as that in which they arise ; that is to say, the outermost fibres of 

 origin from the clavicle are inserted at the uppermost part of the tendon ; the 

 upper fibres of origin from the sternum pass down to the lowermost part of this 

 anterior lamina of the tendon and extend as low as the tendon of the Deltoid and 

 join with it. The posterior lamina of the tendon receives the attachment of the 

 lower half of the sternal portion and the deeper part of the muscle from the costal 

 cartilages. These deep fibres, and particularly those from the lower costal carti- 

 lages, ascend the higher, turning backward successively behind the superficial and 

 upper ones, so that the tendon appears to be twisted. The posterior lamina 

 reaches higher on the humerus than the anterior one, and from it an expansion is 

 given off which covers the bicipital groove and blends with the capsule of the 

 shoulder-joint. From the deepest fibres of this lamina at its insertion an expan- 

 sion is given off which lines the bicipital groove of the humerus, while from the 

 lower border of the tendon a third expansion passes downward to the fascia of the 

 arm. 



Relations. By its anterior surface, with the integument, the superficial fascia, 

 the Platysma, some of the branches of the descending cervical nerves, the mammary 

 gland, and the deep fascia ; by its posterior surface : its thoracic portion, with the 

 sternum, the ribs and costal cartilages, the costo-coracoid membrane, the Subclavius, 

 Pectoralis minor, Serratus magnus, and the Intercostals ; its axillary portion forms 

 the anterior wall of the axillary space, and covers the axillary vessels and nerves, 

 the Biceps and Coraco-brachialis muscles. Its upper border lies parallel with the 

 Deltoid, from which it is separated by a slight interspace in which lie the cephalic 

 vein and humeral branch of the acromial thoracic artery. Its lower border forms 

 the anterior margin of the axilla, being at first separated from the Latissimus dorsi 

 by a considerable interval ; but both muscles gradually converge toward the outer 

 part of the space. 



Dissection. Detach the Pectoralis major by dividing the muscle along its attachment to the 

 clavicle, and by making a vertical incision through its substance a little external to its line of 

 attachment to the sternum and costal cartilages. The muscle should then be reflected outward, 

 and its tendon carefully examined. The Pectoralis minor is now exposed, and immediately 

 above it, in the interval between its upper border and the clavicle, a strong fascia, the costo- 

 coracoul m<>mbr<uie. 



The costo-coracoid membrane is a strong fascia, situated under cover of the 

 clavicular portion of the Pectoralis major muscle. It occupies the interval between 

 the Pectoralis minor and Subclavius muscles, and protects the axillary vessels and 



