THE AXILLARY ARTERY. 767 



splenii. The ascending branches anastomose with the deep and ascending cervical 

 arteries, and with the princeps cervicis of the occipital and the descending branches 

 with the suprascapular and transverse cervical. 



(c) The suprascapular artery (a. transversa scapulae) (Fig. 704), hke the 

 superficial cervical, passes almost directly laterally across the lower part of the pos- 

 terior triangle of the neck. It lies, however, on a somewhat lower level than, and 

 anterior to, the superficial cervical, lying usually behind the clavicle, in front of the 

 subclavian artery, and resting below upon the subclavian vein. It is continued later- 

 ally beneath the trapezius, to which it sends branches, and, having reached the 

 upper border of the scapula, it passes over the transverse ligament of that bone, 

 or occasionally through the suprascapular notch, into the supraspinous fossa. Here 

 it gives branches to the supraspinatus muscle, and, winding around the lateral 

 border of the spine, passes through the scapular notch into the infraspinous fossa, 

 where it breaks up into branches supplying the infraspinatus muscle and anastomos- 

 ing abundantly and widely with the branches of the dorsal scapular artery. 



5. The Transverse CervicaL — The transverse cervical (a. transversa colli) 

 is the only branch which arises from the third portion of the subclavian. It also is 

 directed laterally, parallel with the superficial cervical and suprascapular arteries, 

 about midway between them, but on a much deeper level. It rests upon the anterior 

 surface of the scalenus medius muscle, and upon the trunks of the brachial plexus, 

 and, passing beneath the posterior belly of the omo-hyoid, reaches the lower portion 

 of the levator anguli scapulae, beneath which it terminates by dividing into ascending 

 and posterior scapular branches. 



Branches. — In addition to the two terminal branches, the transverse cervical gives off 

 branches to the trapezius, the supraspinatus, and the levator anguli scapulae muscles. 



{a) The ascending terminal branch (ramus ascendens) passes upward to supply the splenius 

 muscles, and forms anastomoses with the superficial cervical. 



( d ) The posterior scapular artery ( ramus descendens ) descends along the entire length of the 

 vertebral border of the scapula beneath the rhomboid muscles. It supplies these muscles and 

 the serratus posticus superior, and sends branches laterally upon both the dorsal and ventral 

 surfaces of the scapula, supplying the infraspinatus and subscapular muscles and anastomosing 

 with the dorsal scapular and subscapular arteries 



Anastomoses. — The anastomoses which the suprascapular and transverse cer- 

 vical arteries make with the branches of the subscapular artery from the axillary are 

 of considerable importance in the establishment of the collateral circulation from the 

 arm after ligation of the third portion of the subclavian. Additional paths which 

 may be employed for the same purpose are afforded by the anastomoses which 

 occur between the thoracic branches of the axillary artery and the intercostal 

 branches of the superior intercostal, and more especially the perforating branches of 

 the internal mammary. 



Variations. — Very freqxiently indeed the anastomosis which exists between the ascending 

 branch of the transverse and the superficial cervical develops to such an extent that it forms 

 the principal channel by which the blood reaches the posterior scapular from the subclavian, 

 and in such cases the main stem of the transverse cervical disappears, the posterior scapular 

 then becoming a terminal branch of the superficial cervical. This arrangement (Fig. 705) is of 

 such frequent occurrence that it is regarded as the normal one by many authors. When this is 

 done, the name, transverse cervical, is applied to the main stem' of the superficial cervical, the 

 latter term being retained for and limited to the ascending branch of the original arter\'. When 

 this arrangement obtains, there is no branch from the third portion of the subclavian artery, 



THE AXILLARY ARTERY. 



The axillary artery (a. axillaris) (Figs. 704, 705) is the continuation of the 

 subclavian through the axillary space. It begins at the lower border of the first 

 rib, at the apex of the axillary space, and passes downward along the outer 

 wall of the space to the lower border of the teres major, where it becomes the 

 brachial artery. When the arm is abducted to a position at right angles to the 

 axis of the trunk, the artery has an almost straight course, which may be repre- 

 sented by a line drawn from the middle of the clavicle to a point midway between 



