MUSCLES OF THE UPPER EXTREMITY 437 



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

 or both, and from the aponeurosis of the Obliquus externus abdominis. From this 

 extensive origin the fibers converge toward their insertion; those arising from the 

 clavicle pass obliquely downward and lateralward, and are usually separated from 

 the rest by a slight interval; those from the lower part of the sternum, and the 

 cartilages of the lower true ribs, run upward and lateralward; while the middle 

 fibers pass horizontally. They all end in a flat tendon, about 5 cm. broad, which 

 is inserted into the crest of the greater tubercle of the humerus. This tendon con- 

 sists of two laminse, placed one in front of the other, and usually blended together 

 below. The anterior lamina, the thicker, receives the clavicular and the uppermost 

 sternal fibers; they are inserted in the same order as that in which they arise: 

 that is to say, the most lateral of the clavicular fibers are inserted at the upper 

 part of the anterior lamina; the uppermost sternal fibers pass down to the lower 

 part of the lamina which extends as low as the tendon of the Deltoideus and joins 

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

 part of the sternal portion and the deep fibers, i. e., those from the costal cartilages. 

 These deep fibers, and particularly those from the lower costal cartilages, 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 intertubercular groove and blends with the capsule of the shoulder- 

 joint. From the deepest fibers of this lamina at its insertion an expansion is given 

 off which lines the intertubercular groove, while from the lower border of the tendon 

 a third expansion passes downward to the fascia of the arm. 



Variations. The more frequent variations are greater or less extent of attachment to the ribs 

 and sternum, varying size of the abdominal part or its absence, greater or less extent of separation 

 of sternocostal and clavicular parts, fusion of clavicular part with deltoid, decussation in front of 

 the sternum. Deficiency or absence of the sternocostal part is not uncommon. Absence of the 

 clavicular part is less frequent. Rarely the whole muscle is wanting. 



Costocoracaideus is a muscular band occasionally found arising from the ribs or aponeurosis of the 

 External oblique between the Pectoralis major and Latissimus dorsi and inserted into the coracoid 

 process. 



Chondro-epitrochlearis is a muscular slip occasionally found arising from the costal cartilages or 

 from the aponeurosis of the External oblique below the Pectoralis major or from the Pectoralis 

 major itself. The insertion is variable on the inner side of the arm to fascia, intermuscular septum 

 or internal condyle. 



Sternalis, in front of the sternal end of the Pectoralis major parallel to the margin of the sternum. 

 It is supplied by the anterior thoracic nerves and is probably a misplaced part of the pectoralis. 



Coracoclavicular Fascia (fascia coracoclavicularis; costocoracoid membrane; clam- 

 pectoral fascia}. The coracoclavicular fascia is a strong fascia situated under 

 cover of the clavicular portion of the Pectoralis major. It occupies the interval 

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

 and nerves. Traced upward, it splits to enclose the Subclavius, 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. Medially, it' blends with the fascia covering the first two intercostal 

 spaces, and is attached also to the first rib medial to the origin of the Subclavius. 

 Laterally, it is very thick and dense, and is attached to the coracoid process. 

 The portion extending from the first rib to the coracoid process is often whiter and 

 denser than the rest, and is sometimes called the costocoracoid ligament. Below 

 this it is thin, and at the upper border of the Pectoralis minor it splits into two 

 layers to invest the muscle; from the low r er border of the Pectoralis minor it is 

 continued downward to join the axillary fascia, and lateralward to join the fascia 

 over the short head of the Biceps brachii. The coracoclavicular fascia is pierced 

 by the cephalic vein, thoracoacromial artery and vein, and external anterior 

 thoracic nerve. 



