294 



THE MUSCLES. 



Fig. 174. 



volume. Extending from the ninth or tenth rib to the upper extremity of the 

 arm, it at first Ues beneath and against the abdomen, then beneath the chest, 



and at last is comprised between the walls of 

 the latter cavity and the internal face of the 

 anterior limb. 



Form. — It is thin and flat above and below 

 in its posterior third, thicker and depre sed 

 from side to side in its middle third, and 

 narrow and prismatic in its anterior third. 

 Its general form may be compared to that 

 of a somewhat irregular triangle, elongated 

 from before to behind, which would have a 

 very short posterior border, a longer internal 

 or inferior border, and an external or superior, 

 still more extensive. 



Strudure. — It is entirely composed of 

 thick, parallel, fleshy fasciculi, all of which 

 leave the posterior or internal border of the 

 muscle to gain its narrow or anterior extremity. 

 These fasciculi, as they approach the superior 

 border, become longer, and those which proceed 

 from the posterior border commence by 

 aponeurotic fibres. Unfrequent intersections 

 of fibrous tissue exist towards the anterior 

 extremity of the muscle. 



Attachments. — It originates: 1. From the 

 tunica abdominalis by the aponeurotic fasciculi 

 of its posterior border. 2. By its internal 

 border, from the posterior two-thirds of the 

 inferior border of the sternum. It terminates, 

 by its anterior extremity, on the internal 

 tubercle at the head of the humerus, the tendon 

 of origin of the coraco-humeralis, and the 

 fascia enveloping the coraco-radialis. Through 

 the medium of this fascia, it is inserted into 

 the external lip of the bicipital groove formed 

 by the external trochanter, and is united to 

 the two terminal branches of the supra-spinatus 

 muscles (see Figs. 174, 12 ; 181, 5). 



Relations. — Its deep face, which is suc- 

 cessively superior and internal, covers the ex- 

 ternal oblique and the straight muscle of 

 the abdomen, the serratus magnus, lateralis- 

 sterni, and pectoralis parvus, as well as some 

 thoraco-muscular nerves ; all these relations 

 are maintained by means of a loose and 

 abundant connective tissue. Its superior face, 

 which alternately looks downwards and out- 

 wards, responds : to the skin, from which it is separated by a slight cellulo- 

 fibrous fascia ; to the pectoralis transversus ; and to the muscles, vessels, and 



MUSCLES OF THE AXILLARY AND 

 CERVICAL REGIONS. 



1, Portion of the cervical panniculus ; 

 2, anterior portion of the mastoido- 

 humeralis ; 3, posterior portion of 

 ditto; 4, stfrno-maxillaris ; 5, sub- 

 scapulo-hyoideus ; 6, 7, sterno-thyro- 

 hyoideus ; 8, scalenus ; 9, pectoralis 

 anticus; 10, pectoralis transversus; 

 11, pectoralis magnus; 12, portion 

 of the fascia enveloping the coraco- 

 radialis, receiving part of the fibres 

 of the pectoralis magnus; 13, pec- 

 toralis parvus ; 14, its terminal 

 aponeurosis. 



