The terminal branches of the ulnar nerve are two in number, a superficial external, and deep internal. —The former, after a very short course, divides into two branches, a small internal, and large external. The internal branch passes along the ulnar side of the little finger to its extremity, giving filaments in its course to the muscles of the little finger. The external passes obliquely across the flexor tendons for the ring finger, gives a filament to the fourth lumbricus, and one of communication with the median, and over the fourth inter osseous space at a variable distance from its inferior extremity bifurcates : the divisions of the bifurcation being distributed in a similar manner with the median to the opposed sur face of the ring and little finger.
The deep branch is directed backwards and outwards between the abductor minimi digiti, and the flexor brevis to the posterior aspect of the adductor minimi digiti, having first given off on the palm a small branch which sends filaments to these three muscles. It passes downwards in a curved manner, the convexity of the curve looking downwards and inwards, and after a short course passes at an acute angle behind the deep palmar arch of arteries. No branches come off' from its con cavity. From its convexity and back part and outer termination are derived filaments which supply the two inner lumbricales, the palmar hnd dorsal interossei, the adductor and flexor brevis pollicis. The deep or per forating interosseous branches can be traced through the two layers of interossei to the skin on the back of the hand, where they- com municate with the dorsal cutaneous from the radial and ulnar nerves.
The musculo-spiral nerve (radial) • slightly larger than the median, arises from the inner and back part of the plexus, and is formed particularly by the three inferior cervical and first dorsal nerves. The trunk from which it arises also gives origin to the circumflex nerve. It passes at first from before backwards, running behind the ulnar, and in front and below the circumflex nerve, and having crossed the con joined tendons of the teres major, and latissi rnus dorsi, inclines downwards, backwards and outwards to the posterior surface of the hu merus, between it and the long head of the triceps. It continues gradually inclining more outwards, till it reaches the lower third of the arm where it gains the outer aspect of the bone, and here it passes forwards in company with the superior profunda artery, to the an terior and outer aspect of the arm lying in ternal to the outer head of the triceps which it perforates. It is now directed between
the supinator longus and brachialis anticus, and then between the latter and extensor carpi radialis longior, and, having reached the outer and anterior part of the elbow joint, divides into an anterior and posterior terminal branch.
The branches given off from the musculo spiral in the arm are numerous, and may be arranged into { Internal cutaneous. Branch Internal for the internal head of the triceps.
1 Branches for the long head of Posterior the triceps. Outer head and anconmus.
Cutaneous filaments to the External f t_ arm. External cutaneous.
The internal cutaneous is the first branch of the musculo-spiral, and continues for some distance deeply seated to the fascia, which it perforates above the middle of the arm, and descends as one or two filaments along the inner and back part of the arm to the elbow, where they communicate with the posterior filaments of the accessory internal cutaneous.
The branch for the internal head of the tri ceps is the next that is given off. It is a delicate, long nerve, which is directed along the surface of the inner portion of the triceps, running behind the ulnar nerve to within three or four inches of the elbow-joint, when it enters the substance of the muscle.
The branches for the long head of the triceps are numerous, and enter its anterior surface. The superior branch is reflected upwards, and can be traced as far as the axillary origin of the muscle. The inferior or descending branch is the longest, and courses downwards to near the olecranon before entering it.
The branch. jizr the outer head of the triceps and anconous, given off' externally to the branches for the long head, is a long slender nerve. It passes down between the outer and middle head to the outside of the olecranon, sup plying the outer head in its course, and ter minating in the anconmus by entering at its anterior surface.
The external cutaneous branch is given off' below the middle of the arm, as the inusculo spiral is commencing its anterior and outer course. It passes along the outer and back of the arm, and divides into two or three delicate descending filaments which supply the skin, and terminate on the back of the carpus be tween the posterior branches of the external cutaneous, radial, and dorsalis carpi ulnaris with which they communicate.