THE SHOULDER. 467 



between its fasciculi : it is attached, in the middle line, to the front of the 

 sternum; and, above, to the clavicle. It is very thin over the upper part of the 

 muscle, thicker in the interval between the Pectoralis major and Latissimus dorsi, 

 where it closes in the axillary space, and divides at the outer margin of the latter 

 muscle into two layers, one of which passes in front, and the other behind it ; 

 these proceed as far as the spinous processes of the dorsal vertebrae, to Avhich 

 they are attached. At the lower part of the thoracic region this fascia is well 

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



THE SHOULDER. 

 Anterior Thoracic Region. 



Pectoralis major. Pectoralis minor. 



Subclavius. 



The Pectoralis major (Fig. 302) 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 libs, 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 anterior bicipital ridge of the humerus. This 

 tendon consists of two lamin-ae, 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. Another expansion passes downward to the fascia of the arm. 



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

 the Platysma, 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 watl of the axillary space, and 

 covers the axillary vessels and nerves, the Biceps and Coraco-brachialis muscles. 

 Its tipper border lies parallel with the Deltoid, from which it is separated by a 

 slight interspace in which lie the cephalic vein and descending 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 



