THE PORE EXTREMITY. 207 



underneatli flexor metacarpi internus, on the inner sur- 

 face of which it runs, in company with an artery, vein, 

 and nerve, as far as the knee, sending out branches to the 

 flexors in its course, even to fleccor metacarpi externus ; the 

 hranch to this muscle runs through the arch in the u7iion of 

 the ulna to the radius^ and in the passage gives off the medul- 

 lary artery of the radius. 



The axillary plexus of nerves is formed by the union of 

 nerve -fibres from the three posterior cervical and the first 

 dorsal intervertebral nerves, which also receive a branch 

 from the sympathetic system. Emerging between the long 

 and short heads of scalenus, the plexus is thus separated 

 in winding around the first rib from the artery and vein by 

 the lower head of that muscle. From this point collections 

 of fibres pass in company with the corresponding arteries, 

 thus we find the dorsalis scapulce, humeral thoracic, external 

 thoracic, and subscapular nerves, which differ only in arrange- 

 ment from the arteries in that their fibres separate before ar- 

 riving at the parts which they supply, and become thus more 

 diffused over its surface. lu addition to these the axillary 

 plexus gives off the ulnar, spiral and radial nerves, for we find 

 no recognised humeral nerve. The radial runs with the artery 

 of the same name, and below the knee forms the internal 

 metacarpal nerve ; it gives off a branch which runs forwards 

 with the spiral artery to the front of the elbow -joint, 

 where it meets the true spiral nerve, which ran in a back- 

 ward direction, behind the humerus, piercing the fleshy 

 mass of the shoulder by passing between caput parvuni 

 and caput magnum to gain the inferior margin of hume- 

 ralis externus, with which it winds round the external 

 surface of the bone, gains the anterior surface of the joint, 

 and meets the artery, with which it runs to the extensor 

 muscles and the skin covering the front of the limb. The 

 ulnar nerve, from the point of the ulna, sends a loiig hranch 

 down behind the limb underneath ulnaris accessorius, which 

 below the knee becomes the external metacarpal nerve. 



Two important veins are to be found in the region of 

 the shoulder. The humeral vein receives blood from the 

 radial and ulnar veins, and also from a branch which runs 

 to it from just in front of the termination inferiorly of 

 flexor brachii. It then runs up the limb posteriorly 

 placed to the artery and terminates in the axillary vein, 

 which in most respects resembles the artery and opens into 



