784 THE VASCULAR SYSTEM. ~ : 
very short trunk, of considerable size, which passes forwards, pierces the costo- 
coracoid membrane, and terminates beneath the clavicular portion of the pectoralis 
major by dividing into four terminal branches—clavicular, pectoral, humeral, and 
acromial, 
(a) The clavicular branch (ramus clavicularis) is a long slender artery which runs 
upwards and inwards to the sterno-clavicular joint, anastomosing with the superior thoracic, 
with branches of the suprascapular, and with the first perforating branch of the internal 
mammary artery. It supplies the adjacent muscles and the  sterno- clavicular 
articulation. 
(6) The pectoral (ramus pectoralis), or thoracic, is a large branch which descends 
between the two pectoral muscles, to both of which it gives branches and anastomoses with 
the intercostal and lone thoracic arteries. 
(c) The humeral branch (ramus deltoideus) runs outwards to the groove between the 
pectoralis major and the deltoid, in which it descends in company with the cephalic vein 
to the insertion of the deltoid. It anastomoses with the acromial branch and with the 
anterior circumflex artery, and it gives branches to the pectoralis major and deltoid 
muscles and to the skin. 
(d) The acromial branch (ramus acromialis) runs upwards and outwards across the tip 
of the coracoid process to the acromion, where it anastomoses with the last-described — 
branch, with the acromial branches of the suprascapular, and with the posterior circumflex — 
arteries. It gives branches to the deltoid. 
(3) The long thoracic (a. thoracalis pte arises from the second part of 
the axillary, and descends ieee the lower border of the pectoralis minor to 
anastomose with the intercostal and subscapular arteries, and with the pectoral” 
branch of the acromio-thoracic. It supples the adjacent muscles, and sends 
branches to the outer part of the mammary gland, hence it is not infrequently 
called the external mammary artery. 
(4) The alar thoracic is only occasionally present as a distinct branch, but it_ 
is frequently represented by a number of small irregular branches, which may 
either arise from the axillary or from the thoracic and subscapular branches. It is 
distributed to the glands and areolar tissue in the axilla. 
(5) The subscapular artery (a. subscapularis) is the largest branch of the- 
axillary artery. It arises from the third part of the artery, opposite the lower 
border of the subscapularis, along which it descends to the lower angle of the 
scapula and to the inner wall of the axillary space. It is accompanied by the 
second or long subscapular nerve; it supplies the adjacent muscles, and it anasto- 
moses with the posterior scapular, the suprascapular, the long thoracic, and the 
lateral branches of the intercostal arteries, and gives off one named branch, the 
dorsalis scapulee. } 
} 
The dorsalis scapule artery (a. circumflexa scapule) is frequently larger than the 
continuation of the subscapular artery. It arises about one and a half inches (37 mm. y) 
from the commencement of the subscapular trunk, and passes backwards eis the — 
triangular space between the subscapularis above, the teres major below, and the long — 
head of the triceps externally. Turning round, and usually grooving the axillary border 
of the scapula, under cover of the teres ininor, it enters the infraspinous fossa, where it — 
breaks up into branches which anastomose with branches of the posterior scapular and — 
suprascapular arteries. Whilst it is in the triangular space the dorsal artery gives off an — 
infrascapular branch which passes into the subseapular fossa beneath the subscapularis) 
and terminates by anastomosing with the branches of the posterior and suprascapul 
arteries. It also gives off in the same situation a descending branch, which runs down 
wards to the lower angle of the scapula between the teres major and minor muscles, and _ 
small branches are given to the deltoid and scapular head of triceps. 
(6) The posterior circumflex (a. circuinflexa humeri posterior) arises from 
the third part of the axillary artery and passes backwards, accompanied by 
the circumflex nerve, through the EEL onl space, which is bounded by the 
teres minor aboye, the teres major below, the long head of the triceps internally, 
and the humerus externally. It turns round the surgical neck of the humerus | 
under cover of the deltoid muscle, and terminates in numerous branches which — 
