12 THE ANATOMY OP THE HORSE. 



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

 It descends in a nearl}- 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 bj' 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 Cirgdmplex Artery (Plate 6) arises 

 nt 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 mastoidti-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 musculo-spiral nerve, to the front of the elbow-joint, 

 whore it anastomoses with branches of the anterior radial. This 

 branch will not be followed at present. 



iluscuLAR 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 i^ those 

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



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

 of blood which exudes from the smaller cut branches, it will contribute 

 to the neatness and cleanness of the dissection if the dissector will 

 carefully remove the vein and all its branches before he proceeds to 

 follow the nerves. 



The Brachial Plexus. The mode of formation of the plexus has 

 already been explained, and the student will recollect that he has 

 already followed branches from it to ^the levator anguli scapute, 

 serratus magnus, and pectoral muscles, as well as the subcutaneous 



' In Plate the termination of the lacliial artery has been pulled slightly furwajvls in order to 

 show the origin of the anterior radial artery. 



