588 NERVES OF THE UrPEE LIMB. 



on the outer side of the forearm. Communications are established 

 between it and the radial and the external cutaneous branch of the 

 musculo-spiral. 



Varieties. — In some cases it does not perforate the coraco-brachialis muscle. 

 It is frequently found to communicate by a cross branch with, or to be an offset 

 of the median nerve ; and in the latter case, the coraco-brachialis muscle 

 receives a separate branch from the brachial plexus, which may be explained 

 thus, — that the main part of the musculo- cutaneous nerve, instead of piercing 

 the coraco-biachialis muscle, remains adherent to the outer root and trunk of the 

 median. 



Ulnar nerve. — The ulnar nerve, the largest brauch of the inner 

 cord of the brachial plexus, descends on the inner side of the artery 

 of the limb as far as the middle of the arm, then turns backwards 

 through the internal intermuscular septum with the inferior profunda 

 artery, to reach the interval between the olecranon and the inner 

 condyle of the humerus. From the axilla to this place it is covered 

 only by the fascia, and it may be felt through the integument a little 

 above the elbow. It here passes between the two heads of the flexor 

 carpi ulnaris, and it remains concealed by that muscle as far as the 

 middle of the forearm ; it thence extends in a straiglit course along the 

 outer margin of the muscle, between it and the ulnar artery, to the 

 outer side of the pisiform bone. Above the wrist it gives off a large 

 dorsal branch to the hand, and continuing onwards it enters the palm 

 on the surface of the annular ligament, and divides into muscular and 

 cutaneous branches. 



The ulnar nerve usually gives ofP no branches in the upper arm. 



A. Branches iif the forearm : — 



a. Articular filaments are given to the elbow-joint as the nerve passes behind 

 it. Some filaments are also given to the wrist-joint. 



I). Muscular branches. — One branch enters the upper part of the flexor carpi 

 idnaris, and another supplies the t-u'o inner divisions of the deep flexor of the 

 Angers. 



c. Cutaneous branches to the forearm. — These two small nerves arise about the 

 middle of the forearm by a common trunk. One pierces the fascia, and turning 

 doN\Tiward, joins a branch of the internal cutaneous nerve. This branch is often 

 absent. The second, a palmar branch, lies on the ulnar artery, which it accom- 

 panies to the hand. This little nerve gives filaments around the vessel, and 

 ramifies in the integument of the hand, joining in some cases with other cutaneous 

 offsets of the ulnar or median nerve. 



d. Dorsal branch to the hand — This large offset, leaving the trunk of the ulnar 

 nerve two or three inches above the wrist, winds backwards beneath the flexor 

 cari)i uhiaris and divides into branches ; one of these ramifies on the inner side 

 of the little finger, another divides to supply the contiguous sides of that finger 

 and the ring finger, while a third joins on the back of the metacaiinis with the 

 branch of the radial nerve which supplies the contiguous sides of the ring and 

 middle finger. The several posterior digital nerves, now described, are iinited 

 with twigs directed backwards from the anterior digital nerves of the same 

 fingers. 



B. Palmar branches : — 



a. The deej) branch separates from the trunk beyond the annular ligament, and, 

 dipping do^\^l through the muscles of the little finger in company with the deep 

 branch of the ulnar artery, it follows the course of the deep palmar arch across 

 the hand. It supplies the short muscles of the little finger as it pierces them ; 

 and as it lies across the metacarpal bone, it distributes two branches to each. 



