FASCIAE AND MUSCLES OF THE PECTOEAL REGION. 369 



connected to the vertebral margin of the scapula, for the most part, by loose 

 areolar tissue, and is fixed to the bone at its extremities, above near the base of 

 the spine, and below at the inferior angle. 



The rhomboid muscles are concealed to a large extent by the trapezius. The 

 lower part of the rhomboideus major is superficial in the triangle of auscultation. 

 The muscles cover the serratus posterior superior and vertebral aponeurosis. 



Nerve-Supply. The rhomboid muscles are supplied- by the dorsal scapular nerve from the 

 brachial plexus (C. 5.), which supplies branches in the deep surface of the muscles. 



Action. The rhomboid muscles elevate and draw backwards the vertebral margin of the 

 scapula. 



THE FASCI/E AND MUSCLES OF THE 

 PECTORAL REGION. 



FASCLE. 



The superficial fascia of the chest usually contains a quantity of fat, in which 

 the mamma is embedded. The origin of the platysma muscle lies beneath its 

 superior part. 



The deep fascia is attached above to the clavicle, and in the median plane to 

 the sternum. Below it is continuous with the fascia of the abdominal wall. It 

 gives origin to the platysma and invests the pectoralis major. At the lateral 

 border of the great pectoral muscle it is thickened, and forms the floor of the 

 axillary space (axillary fascia), continued posteriorly on to the posterior fold of 

 the axilla and laterally into connexion with the deep fascia of the arm. 



Costo-Coracoid Membrane. Beneath the pectoralis major a deeper stratum of 

 fascia invests the pectoralis minor muscle. At the superior border of this muscle 

 it forms the costo-coracoid membrane, which passes upwards to the inferior border 

 of the subclavius muscle, where it splits into two layers, attached in front of and 

 behind that muscle to the borders of the inferior surface of the clavicle. The 

 membrane traced medially along the subclavius muscle is attached to the first 

 costal cartilage ; passing laterally along the upper border of the pectoralis 

 minor it reaches the coracoid process. The part of the membrane extending 

 directly between the first costal cartilage and the coracoid process is thickened 

 and forms the costo-coracoid ligament. The costo-coracoid membrane is otherwise 

 thin and of comparatively small importance. It is pierced by the cephalic vein, 

 thoraco-acromial artery and vein, and branches of the lateral anterior thoracic 

 nerve. By its deep surface it is connected to the sheath of the axillary vessels. 



At the inferior border of the pectoralis minor there is a further extension of the 

 deep fascia beneath the pectoralis major. It passes downwards to join the fascia 

 forming the floor of the axilla, and is continued laterally into the fascia covering 

 the biceps and coracobrachialis muscles. 



MUSCLES OF THE PECTORAL REGION. 



The anterior muscles connecting the upper limb to the axial skeleton comprise 

 the pectoralis major, pectoralis minor, subclavius, serratus anterior, and sterno- 

 cleido-mastoid. The last is described in a later section (p. 458). 



M. Pectoralis Major. The pectoralis major is a large fan-shaped muscle 

 arising in three parts : (1) a pars clavicularis arising from the anterior aspect 

 of the clavicle in its medial half or two-thirds (Figs. 327, p. 366, and 331, p. 371) ; 

 (2) a pars sternocostalis, the largest part of the muscle, arising from the anterior 

 surface of the manubrium and body of the sternum by tendinous fibres decussat- 

 ing with those of the opposite muscle (Fig. 330, p. 370), and, more deeply, from 

 : the cartilages of the first six ribs; (3) a pars abdominalis, a small and separate 

 slip, arising from the aponeurosis of the obliquus abdominis externus muscle. The 

 ; abdominal slip, at first separate, soon merges with the sterno-costal portion, but a 

 distinct interval usually remains between the two first-named parts of the muscle. 



25 



