ULNAR NERVE. 587 
are placed superficial to the digital arteries, and are distributed to the sides and 
front of the fingers. Each nerve supplies one or more dorsal branches, which 
supply the skin on the dorsal aspect of the terminal phalanx of the thumb and 
the two distal phalanges of the first two and a half fingers, thus making up for 
the deficiency of the radial nerve in these situations. 
ULNAR NERVE. 
The ulnar nerve (n. ulnaris) arises from the inner cord of the brachial plexus, 
from the eighth cervical and first thoracic nerves. In the axilla it lies between the 
axillary artery and vein, and behind the internal cutaneous nerve; in the upper 
half of the upper arm it les on the inner side of the brachial artery in front of the 
triceps muscle. In the lower half of the arm it is separated from the brachial 
artery; and passing behind the intermuscular septum, and in front of the inner 
head of the triceps in company with the inferior profunda artery, it reaches the 
interval between the internal condyle of the humerus and the olecranon process. 
It is here protected by an arch of deep fascia stretching between the internal 
condyle and the olecranon process. It enters the forearm between the humeral 
and ulnar origins of the flexor carpi ulnaris, and courses downwards between the 
flexor carpl ulnaris and flexor profundus digitorum. In the lower half of the 
forearm it becomes comparatively superficial, lying on the inner side of the ulnar 
artery beneath the tendon of the flexor carpi ulnaris. Just above the anterior 
annular ligament of the wrist, and external to the pisiform bone, it pierces the 
deep fascia in company with the artery and passes into the hand over the anterior 
annular ligament. Reaching the palm it divides beneath the palmaris brevis 
muscle into its two terminal branches. 
Communications. — (1) The ulnar nerve communicates in some cases with the 
median nerve in the forearm ; (2) with the internal cutaneous and sometimes the median 
nerve by its palmar cutaneous branch ; (3) with the cutaneous part of the median nerve 
in the palm by means of its terminal cutaneous branch; (4) with the radial nerve on 
the dorsum of the hand by means of its dorsal branch. 
Branches.—The ulnar nerve gives off no branches till it reaches the forearm. 
In the forearm it gives off articular, muscular, and cutaneous branches. The 
articular branch is distributed to the elbow joint and arises as the nerve passes 
behind the internal condyle. 
The muscular branches arise as soon as the nerve enters the forearm. They are 
distributed to the muscles between which the ulnar nerve lies—the flexor carpi 
wlnaris and the inner half of the flexor profundus digitorum. 
The cutaneous branches are two in number, palmar and dorsal. 
The palmar cutaneous branch is variable in size and position. It pierces the 
deep fascia in the lower third of the forearm and passes to the hypothenar 
eminence and palm of the hand, to which it is distributed. It gives branches to 
the ulnar artery, and communicates often with the internal cutaneous and palmar 
branch of the median nerve. 
The dorsal cutaneous branch is much larger (Fig. 433, p. 588). It arises from the 
ulnar nerve in the middle third of the forearm ; and, directed obliquely downwards 
and backwards beneath the tendon of the flexor carpi ulnaris, it becomes cutaneous 
on the inner side of the forearm in its lower fourth. It passes on to the back of the 
hand, and after giving off branches to the skin of the wrist and hand, which com- 
municate with the radial nerve, it terminates in two branches, to supply the little 
finger and half the ring-finger in the following way :—the inner branch courses along 
the inner side of the dorsum of the hand and little finger: the outer branch subdiv ides 
at the cleft between the ring and little fingers to supply the adjacent sides of these 
fingers ; this branch communicates with the radial nerve. The nerve may supply 
two and a half fingers on the dorsum of the hand. 
In the palm the ulnar nerve supplies a small muscular branch to the palmaris 
brevis muscle, and then subdivides into its terminal branches, which are named 
superficial and deep. 
