TEE BEACH I AL PLEXUS. 865 



artery, from which it is separated by the ulnar nerve. Arriving at the deep 

 humeral artery — which it leaves on the outside — it passes behind the humerus with 

 the divisions of that artery, and enters between the caput magnum and brachialis 

 anticus. After creeping along the posterior border of the latter muscle, it gains 

 the anterior face of the ulna-radial articulation, where it is covered by the two 

 principal extensors of the metacai-pus and the phalanges, and, meeting the radial 

 artery, accompanies it on to the oblique extensor of the metacarpus. There it 

 terminates by two branches, which enter the texture of that muscle. 

 In its course, it successively gives off — 



1. Before leaving the internal face of the limb, to pass beneath the mass of 

 extensor muscles of the forearm, a very thick fasciculus, composed of several 

 branches — descending and ascending. The latter bend round the terminal 

 tendon common to the latissimus dorsi and teres major, to become lost in the 

 body of the great extensor ; the others reach either the long and middle 

 extensors, or the inferior portion of the principal muscle — the large extensor. 



2. Behind the arm, filaments to the caput medium and anconeus, and 

 several cutaneous ramuscules, disengaged from beneath the former muscle, 

 that descend beneath the skin on the anterior face of that part. 



3. In the antibrachial region, branches to the extensor metacarpi magnus 

 and flexor metacarpi externus, and the two extensors of the digit. 



In brief, we see that the radial nerve is distributed to, and therefore 

 stimulates, the whole mass of the extensor muscles of the forearm and foot, 

 besides a flexor of the latter ; and that it endows the integument of the anterior 

 antibrachial region with sensibility. 



13. Ulnar or Cubito-cutaneous Nerve (Figs. 465, 18 ; 466, 5). 



Chiefly formed by fibres from the dorsal pairs, this nerve — less considerable in 

 volume than the preceding — passes backward and downward, and places itself 

 behind the humeral artery, which it accompanies to below the origin of the deep 

 humeral. After crossing the latter vessel, it passes between the scapulo-ulnaris 

 and caput parvum, and gains the inner side of the elbow, running over the 

 epicondyle, below the ulnar band of the oblique flexor of the metacarpus. It 

 follows the posterior border of that muscle to near the pisiform bone, where it 

 terminates by two branches. In the latter part of its course, it lies beneath the 

 antibrachial aponeurosis, accompanied by a division of the epicondyloid artery. 



One of the two branches — the cutaneous (Fig. 466, 6) — crosses the space 

 between the terminal tendons of the external and obhque flexor muscles of the 

 metacarpus, as well as the antibrachial aponeurosis, to expend itself in several 

 ascending horizontal and descending filaments, beneath the skin of the forearm, 

 the anterior face of the knee, and the external side of the cannon. The other 

 branch, with a ramuscule from the median nerve, constitutes the external plantar 

 nerve. 



In its course, the ulnar nerve gives off two fasciculi of collateral branches. 

 The first (Fig. 465, 19) is detached from the principal trunk a little above the 

 epicondyloid artery, and passes backward and downward between the scapulo- 

 ulnaris and the anterior superficial pectoral — supplying some filaments to the 

 latter — traverses it to become subcutaneous, and to be distributed to the skin of 

 the forearm, beneath the elbow {internal brachial cutaneous). The second arises 

 at the epicondyle, and is destined to all the muscles of the posterior antibrachial 

 region, except the external and internal flexors of the metacarpus. 



