374 MUSCLES AND FASCIA. 



their point of insertion. 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 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 ; the posterior lamina re- 

 ceiving the attachment of the lower half of the sternal portion. From this 

 arrangement it results, that the fibres of the upper and middle portions of the 

 muscle are inserted into the lower part of the bicipital ridge ; those of the lower 

 portion, into the upper part. The tendon, at its insertion, is connected with 

 that of the Deltoid ; it sends up an expansion over the bicipital groove to the 

 head of the humerus ; another backwards, which lines the groove ; and a third 

 to the fascia of the arm. 



Relations. By its anterior surface, -with the Platysma, the mammary gland, 

 the superficial fascia, and integument. By its posterior surface its thoracic por- 

 tion, with the sternum, the ribs and costal cartilages, 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. 

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

 cephalic vein and descending branch of the thora'cico-acromialis 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 towards the outer part of the space. 



Peculiarities. In muscular subjects, the sternal origins of the two Pectoral muscles are 

 separated only by a narrow interval ; but this interval is enlarged where these muscles are ill 

 developed. Yery rarely, the whole of the sternal portion is deficient. Occasionally, one or two 

 additional muscular slips arise from the aponeurosis of the External Oblique, and become united 

 to the lower margin of the Pectoralis Major. A slender muscular slip is occasionally found 

 lying parallel with the outer margin of the sternum, overlapping the origin of the Pectoral 

 muscle. It is attached, by one end, to the upper part of the sternum, near the origin of the 

 Stern o-mastoid ; and, by the other, to the anterior wall of the sheath of the Rectus Abdominis. 

 It has received the name " Rectus Sternalis." 



DisKection. 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 out- 

 wards, and its tendon carefully examined. The Pectoralis Minor is now exposed, and imme- 

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

 costo-coracoid membrane. 



The costo-coracoid membrane protects the axillary vessels and nerves ; it is 

 very thick and dense externally, where it is attached to the coracoid process, 

 and is continuous with the fascia of the arm ; more internally, it is connected 

 with the lower border of the clavicle, as far as the sternal extremity of the first 

 rib: traced downwards, it passes behind the Pectoralis Minor, surrounding, in 

 a more or less complete sheath, the axillary vessels and nerves ; and above, it 

 sends a prolongation behind the Subclavius, which is attached to the lower 

 border of the clavicle, and so incloses the muscle in a kind of sheath. The 

 costo-coracoid membrane is pierced by the cephalic vein, the thoracico-acro- 

 mialis artery and vein, superior thoracic artery, and anterior thoracic nerve. 



The Pectoralis A/i/mr (Kig. 237) is a thin, flat, triangular muscle, situated at 

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

 tendinous digitations, from the upper margin and outer surface of the third, 

 fourth, and fifth ribs, near their cartilages, and from the aponeurosis covering 

 the Intercostal muscles; the fibres pass upwards and outwards, and converge 

 to form a (hit tendon, which is inserted into the anterior border of the coracoid 

 process of the scapula. 



Relations. By its anterior surface, with the Pectoralis Major, and the superior 

 thoracic vessels and nerves. By its posterior surface, with the ribs, Intercostal 

 muscles, Serratus Magnus, the axillary space, and the axillary vessels and 

 nerves. Its upper border is separated from the clavicle by a triangular inter- 

 val, broad internally, narrow externally, bounded in trout by the costo-coracoid 



