FORE-ARM. 



361 



FORE-ARM, (Surgical anatomy), (Anti- 

 brachium ; Fr. Avant-bras ; Germ, der V order- 

 arm). This term is applied to that portion 

 of the upper extremity which is situated be- 

 tween the elbow and wrist-joint. 



In the well-formed male all the muscles of 

 this region, but especially the supinators, from 

 the fascia which covers them being extremely 

 thin, when thrown into action stand out in 

 strong relief, giving an appearance of great 

 power concentrated within a small space. In 

 the female, on the contrary, the fore-arm, from 

 the great preponderance of adipose tissue, 

 presents a swelling outline and rounded form, 

 not the less beautiful, perhaps, from indicating 

 deficiency of muscular energy, and conveying 

 the idea of softness and dependence. 



The usual and least constrained position of 

 the fore-arm is with the hand between prona- 

 tion and supination, that is, with the palm 

 of the hand inwards and the dorsum outwards; 

 but for the purpose of anatomical description 

 the palm of the hand is supposed to face for- 

 wards and the dorsum backwards, the fore-arm 

 being extended. In this position the fore- 

 arm obviously differs from the arm in being 

 wider from side to side than from before back- 

 wards. Superiorly it presents in front a very 

 slightly convex surface, but inferiorly there is 

 formed by the flexor tendon a distinct central 

 projection, which is bounded by the flexor carpi 

 radiahs on the radial side, and by the flexor carpi 

 ulnaris on the ulnar. 



The posterior surface of the fore-arm is more 

 irregularly convex than the anterior; the greatest 

 convexity is nearer the ulnar than the radial 

 edge, and is formed by the olecranon above 

 and the shaft of the ulna below, which is 

 covered only by the skin superiorly. A con- 

 siderable depression may be observed, bounded 

 on the inner side by the olecranon, and on 

 the outer by the supinators ; in this depression 

 the outer condyle may be felt. To the inner 

 side of the olecranon there is a corresponding 

 but much smaller depression, in which the 

 inner condyle is situated. For about three 

 inches above the wrist-joint the fore-arm pos- 

 teriorly is slightly concave in the centre in 

 consequence of the marked projection of the 

 ulna and radius on either side. In the motions 

 of pronation and supination the shape of the 

 fore-arm is considerably changed; but as no 

 practical advantage can attend a detailed ac- 

 count of the changes undergone, we shall not 

 dwell upon them here. 



The parts composing the fore- arm are as fol- 

 low : the radius and ulna, the muscles of the hand 

 and fingers, the radial and ulnar arteries with 

 their branches, the venae satellites of these 

 arteries and the subcutaneous veins, the radial, 

 ulnar, median, and cutaneous nerves, the ab- 

 sorbent vessels, a quantity of cellular and 

 adipose tissue, various aponeuroses, and the 

 common : 'eguments. 



The t.^guration, relative position, and 

 connection of the bones of the fore-arm have 

 been described in the article EXTREMITY. 

 They \. ve together in the flexion and exten- 



sion of the fore-arm on the os humeri at the 

 elbow-joint, under the influence of the biceps 

 flexor cubiti and brachialis anticus, and the 

 triceps extensor cubiti and anconeus. 



In the motions of supination and pronation 

 the radius is always rolled upon the ulna, 

 the latter remaining perfectly fixed, though 

 this fact has been disputed in consequence of 

 the thick sacciform ligament of the wrist and 

 the tendon of the extensor carpi ulnaris being 

 felt to roll under the finger when placed on 

 the inferior extremity of the ulna during the 

 motion of rotation and supination, and thus 

 communicating the sensation of a motiou in 

 the ulna itself. 



The skin of the fore-arm differs considerably 

 on the dorsal and anterior aspects. On the 

 former it is coarse and comparatively rough, 

 containing numerous small hairs ; on the latter 

 it is smooth and more delicate, and the adipose 

 tissue being more abundant on the anterior, 

 the whole surface is more even, while on the 

 posterior the extensor muscles of the hand 

 and fingers, being slightly covered, project 

 considerably. Neither of the regions, however, 

 contain so much fat as most other parts of the 

 body. 



The superficial veins which are subject to 

 the greatest variety, are usually more distinct 

 and numerous on the dorsal aspect, particularly 

 at the lower part. 



The subcutaneous nerves, which are very 

 numerous, are derived from the following 

 sources : 1st, the internal cutaneous nerve, 

 which is one of the divisions of the axillary 

 plexus; 2dly, the cutaneous branch of the 

 radial ; 3dly, the musculo-cutaneous. 



The internal cutaneous nerve divides into 

 two branches in the upper arm, in which 

 region it accompanies the basilic vein. These 

 two branches penetrate the fascia separately 

 above the elbow-joint, and the one, the an- 

 terior branch, descends on the front of the 

 fore-arm, the other, the posterior, on the back 

 of it. The anterior branch usually passes 

 behind the basilic vein, sending a small twig 

 or two anterior to it. Its course is continued 

 to the wrist-joint, supplying the skin on the 

 anterior and inner side throughout; the pos- 

 terior division accompanies the basilic vein, 

 and may be always traced to the back part 

 of the wrist. 



The small branches of this nerve, which 

 cross in front of the basilic or median basilic 

 vein, are occasionally wounded in the opera- 

 tion of venesection ; an accident which gene- 

 rally excites considerable inflammation, with 

 severe constitutional irritation, symptoms which 

 are sometimes erroneously attributed to the 

 action of a foul lancet. 



The skin on the anterior surface of the outer 

 half of the fore-arm is supplied with nerves 

 by the external cutaneous nerve, a division of 

 the axillary plexus : it is a deep-seated mus- 

 cular nerve in the upper arm and penetrates 

 the fascia, becoming subcutaneous anterior 

 and a little below the elbow-joint. In this 

 situation it is posterior to the median cephalic 



