12 THE ANATOMY OF THE HORSE. 



major muscles ; and, disappearing between these muscles, it ascends 

 behind the glenoid border of the scapula, as far as its dorsal angle. 

 It gives off a considerable number of vessels that cannot at this stage 

 be completely followed, but near its origin it will be seen to throw off 

 a branch which runs upwards and backwards on the latissimus dorsi 

 (Plate 5). 



The Brachial Artery (Plates 5 and 6) is the direct continuation of 

 the axillary, which changes its name when it passes on to the teres 

 major. It descends in a nearly vertical direction to the lower extremity 

 of the humerus, where, above the inner condyle, it divides to form the 

 anterior and posterior radial arteries.^ In its course it crosses the 

 direction of the humerus obliquely, and rests successively on the 

 tendons of the teres major and latissimus dorsi, the small head of 

 the triceps, and the bone. In front of it is first the coraco-humeralis, 

 and then the biceps ; but these are separated from it by the median 

 nerve, which is in close contact with the vessel. Behind the artery is 

 the satellite vein, posterior to which is the ulnar nerve. Its collateral 

 branches are : the pre-humeral, the deep humeral, the ulnar, the 

 nutrient artery of the humerus (sometimes), and innominate muscular 

 branches. 



The Pre-humeral or Anterior Circumflex Artery (Plate 6) arises 

 at the tendon of the teres major, and passes in front of the humerus, 

 between the upper and lower insertions of the coraco-humeralis, to 

 terminate in the biceps or the mastoido-humeralis. Some of its fine 

 twigs may anastomose with divisions of the posterior circumflex. 



The Deep Humeral Artery (Plates 5 and 6) arises at the lower 

 border of the latissimus dorsi tendon, and soon splits into three or 

 four branches, the larger of which perforate the large head of the 

 triceps extensor cubiti, while the smaller supply the small and 

 medium heads of the same muscle. A branch is continued round 

 behind the humerus, in company with the musoulo-spiral nerve, to the 

 front of the elbow-joint, where it anastomoses with branches of the 

 anterior radial. This branch will not be followed at present. 



Muscular Branches of the Brachial. The largest and most constant 

 of these is a vessel of considerable size which penetrates the lower part 

 of the biceps (Plate 6). 



The Ulnar artery and the two terminal branches of the brachial will 

 be followed in the dissection of the fore-arm. 



The Brachial Vein is a large vessel which ascends behind the artery, 

 and receives branches that for the most part correspond to those of the 

 artery. It also receives the subcutaneous thoracic or spur vein. 



Directions. — As the brachial vein generally contains a large quantity 



1 In Plate 6 the termination of the brachial artery has been pulled slightly forwards 

 in order to show the origin of the anterior radial arterv. 



