196 MYOLOGY, OR ANATOMY OF MUSCULAR SYSTEM 



the clavicular portion of the pectoralis major, bridging in the 

 interval between the upper border of the pectoralis minor 

 muscle and the subclavius muscles. Above it splits, and is 

 attached to the clavicle, one layer in front of the subclavius 

 muscle, the other layer behind it. Internally it blends with 

 the fascia covering the first two intercostal spaces, and is 

 also attached to the first rib, internal to the origin of the sub- 

 clavius muscle. Externally it is attached to the coracoid 

 process. This latter portion of the membrane is called the 

 costocoracoid ligament, extending from the first rib to the 

 coracoid process and blended with the subclavius muscle. 

 Below, the costocoracoid membrane splits at the upper border 

 of the pectoralis minor muscle, invests it, and from the lower 

 border the single layer is continued downward to join the fascia 

 covering the biceps muscle and axillary fascia. The cephalic 

 vein, acromiothoracic vessels, superior thoracic artery, and 

 external anterior thoracic nerve pierce the costocoracoid mem- 

 brane. It also sends a slip upward behind the clavicle to 

 blend with the deep cervical fascia and the sheath of the 

 axillary vessels. 



The Anterior Thoracic Region 



M. pectoralis major, two portions, clavicular and 

 the clavicular portion rises from the inner half of the anterior 

 surface of the clavicle and sternoclavicular capsule, the sterno- 

 costal from the sternum (superficial part, Henle), from the 

 upper six rib cartilages (deep part, Henle) and from the anterior 

 sheath of the rectus and external oblique aponeurosis. The 

 fibers converge to be inserted by two tendons, united along 

 the lower margin, into the external bicipital ridge; the clavic- 

 ular and upper sternocostal parts form one tendon with straight 

 fibers; the lower sternocostal part twists so that its lowest 

 fibers are inserted highest; a bursa separates this from the 

 other anterior tendon. This posterior layer also gives off 

 three expansions one over the biceps tendon to the capsule 

 of the shoulder-joint, one lining the bicipital groove, and one 

 to the deep fascia of the arm. 



1. M. xnl)c1<ipi;ujf rises from the groove on the under surface 

 of the clavicle and recess between the conoid and trapezoid 



