THE POSTERIOR RADIAL ARTERY 559 



Not rarely it arises below the middle of the humerus and passes upward between the biceps 

 and coraco-brachialis. In these cases a small branch for the coraco-brachialis is usually given 

 off at the usual point of origin of the anterior circumflex. 



4. The deep brachial artery (A. profunda brachii) is a large but short trunk 

 which arises usually about the middle of the humerus. It passes backward and 

 divides into several branches which supply the triceps, tensor fasciae antil^rachii, 

 anconeus, and brachialis. A branch runs in the musculo-spiral groove with the 

 radial nerve to the front of the elbow joint and anastomoses with the anterior 

 radial. A slender branch passes down along the external border of the extensor 

 carpi and supplies cutaneous twigs. Anastomoses occur with the ulnar and recur- 

 rent interosseous arteries. 



The point of origin is inconstant and it is not uncommon to find two arteries instead. 

 Often a large branch for the posterior deep pectoral muscle is detached close to the origin or arises 

 from the brachial directly. 



5. Muscular branches (Rami musculares) are distributed to the teres major, 

 deep pectoral, coraco-brachialis, and biceps. The largest and least variable of 

 these supplies the lower part of the biceps. 



6. The ulnar artery (A. collateralis ulnaris superior) arises a little below the 

 nutrient foramen of the humerus and passes downward and backward along the 

 lower edge of the internal head of the triceps under cover of the brachial vein and 

 the tensor fascia antibrachii. It gives l)ranches to these muscles, the posterior 

 superficial pectoral, the cul)ital lymph glands, panniculus, and skin. At the inter- 

 nal epicondyle of the humerus it is joined by the ulnar nerve and turns downward 

 under the ulnar head of the flexor carpi medius. It continues with the vein and 

 nerve under the deep fascia of the forearm ])etween the ulnar and humeral heads of 

 the perforans, and in the distal half of the region l)etw(^en the external and middle 

 flexors of the carj^us. It unites just above the carpus (under cover of the flexor 

 carpi externus) with a branch of the radial artery, with which it forms the supra- 

 carpal arch. It detaches small collaterals to the muscles along which it passes 

 and terminal twigs to the out(n- surface of the carpus. 



7. The nutrient artery of the humerus (A. nutritia humeri) is a short vessel 

 which enters the nutrient foramen of the humerus. It often arises from the ulnar. 



8. The anterior radial artery (A. collateralis radialis inferior) passes downward 

 and a little outward on the anterior face of the humerus under cover of the biceps 

 and brachialis to the front of the elbow joint, where it is joined by the radial nerve. 

 It then descends on the anterior surface of the radius under cover of the anterior 

 extensor of the digit to the carpus, where it concurs in the formation of the rete 

 carpi dorsale, anastomosing with the posterior radial and interosseous arteries. It 

 supplies branches to the elbow joint, the l)iceps, brachialis, and the extensors of 

 the carpus and digit. A cutaneous branch emerges between the distal end of the 

 biceps and the brachialis. 



THE POSTERIOR RADIAL ARTERY 

 The posterior radial or median artery (A. mediana) is the direct continuation 

 of the brachial. It passes downward and slightly backward, at first on the inner 

 surface of the humerus, and then over the capsule and internal lateral ligament 

 of the elbow joint, under cover of the posterior superficial pectoral muscle.^ Below 

 the elbow it dips under the flexor carpi internus and passes down the inner part of 

 the posterior surface of the radius. In the distal part of the forearm it inclines 

 backward and is separated from the radius by the reinforcing band (Caput tendin- 

 eum) of the superficial flexor of the digit and is continued by the large metacarpal 

 artery. 



' The pulse can be taken where the artery lies on the lateral ligament, since the pectoral 

 muscle is thin here. 



