1 68 THE SURGICAL ANATOMY OF THE HORSE 



The branches which this portion of the axillary artery gives off are : 



1. T/ie Exter/m/ Thoracic Artery. — This is frequently termed the 

 external mammary artery. It is given off by the axillary near the 

 anterior border of the first rib, and takes a course backwards on the deep 

 face of the pectoral muscles, to which its collateral branches are dis- 

 tributed. Its volume is subject to a considerable degree of variation, 

 and cases have been reported in which the artery was entirely absent. 

 It o-ives off a long and slender branch, which follows the course of the 

 spur vein and is distributed to the panniculus carnosus. 



2. The Inferior Cervical Artery. — This branch is given off by the 

 axillary opposite the point at which the external thoracic artery is 

 detached. It is found in the channel between the two jugular veins, 

 immediately above the prepectoral lymphatic glands. After a very short 

 course it divides into two branches. One of these ascends in the groove 

 between the mastoido-humeralis and subscapulo-hyoideus muscles, and is 

 distributed to these and also to the levator anguli scapuls and anterior 

 superficial pectoral. The other, which is the inferior branch, takes a 

 course downwards, and is found superficially placed in the groove 

 between the mastoido-humeralis and anterior deep pectoral, where it runs 

 alongside the cephalic vein. It is distributed to the pectorals and 

 mastoido-humeralis. 



3. The Suprascapular Artery. — This is a slender vessel which is given 

 off by the axillary before the latter crosses the tendon of the sub- 

 scapularis muscle. It is slightly tortuous, and taking an upward course on 

 the subscapularis, it passes into the interspace between this muscle and the 

 supraspinatus, to wind round the coracoid border of the scapula and gain 

 its dorsal aspect. Its terminal branches are distributed to the inferior 

 portions of the supraspinatus and infraspinatus muscles. 



4. The Subscapular Artery. — Where the axillary artery crosses the 

 line of apposition of the subscapularis and teres major muscles it gives 

 off a branch which is of considerable diameter although very short. 

 This is the subscapular artery, and it comes off at right angles to the 



