OF THE THORACIC REGION. 



379 



nerves. Traced upward, it splits to enclose the Subclavius muscle, and its two 

 layers are attached to the clavicle, one in front of and the other behind the muscle ; 

 the latter layer fuses with the deep cervical fascia and with the sheath of the 

 axillary vessels. Internally, it blends with the fascia covering the first two inter- 



FIG. 229. Muscles of the chest and front of the arm. Superficial view. 



costal spaces, and is attached also to the first rib internal to the origin of the Sub- 

 cl:ivius muscle. Externally it is very thick and dense, and is attached to the cora- 

 coid process. The portion extending from its attachment to the first rib to the 

 coracoid process is often whiter and denser than the rest ; this is sometimes called 

 the costo-coracoid ligament. Below, it is thin, and at the upper border of the Pec- 

 toralis minor it splits into two layers to invest the muscle ; from the lower border of 

 the Pectoralis minor it is continued downward to join the axillary fascia, and out- 

 ward to join the fascia over the short head of the Biceps. The costo-coracoid mem- 

 brane is pierced by the cephalic vein, the acromial thoracic artery and vein, super- 

 ior thoracic artery, and anterior thoracic nerves. 



The Pectoralis minor (Fig. 230) is a thin, flat, triangular muscle, situated at 

 the upper part of the thorax, beneath the Pectoralis major. It arises by three 



