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MUSCLES OF THE FORE-ARM. 



the flexor communis digitorum sublimis. The 

 relation of this muscle to the ulnar artery has 

 induced some anatomists to denominate it 

 muscle satellite de Varttre cubitale. 



In addition to its power as a flexor of the 

 hand on the fore-arm, this muscle adducts the 

 hand, drawing it towards the mesial line. 



b. The deep layer of muscles. These are 

 three in number, the flexor longus proprius 

 pollicis, flexor communis digitorum profundus 

 perforans, and the pronator quadratus. A por- 

 tion of the supinator radii brevis is also found 

 in it. 



1. The flexor longus proprius pollicis, 

 Sffimm. ( Radio -phalangettien du pouce, 

 Chauss.) This muscle, situated most exter- 

 nally, arises by two heads ; one, narrow, rounded, 

 tendinous, and fleshy, from the inner condyle 

 of the humerus; the other, broad and fleshy, 

 from the front of the radius, below the insertion 

 of the biceps and supinator radii brevis, and 

 from the interosseal ligament, extending as low 

 down as the insertion of the pronator quadratus. 

 Its tendon, first formed on its internal and 

 anterior edge, descends behind the annular 

 ligament of the wrist-joint, and taking its 

 course between the two heads of the flexor 

 brevis pollicis, is inserted into the last phalanx 

 of the thumb. 



This muscle is covered anteriorly by the 

 supinator radii longus and extensor carpi radialis 

 longior, except at the lower part, where it is 

 simply covered by the deep fascia on which 

 the radial artery lies. To its inner side is the 

 flexor digitorum profundus. 



This muscle is a flexor of the last phalanx 

 of the thumb, a powerful and important muscle 

 in grasping objects. 



2. Flexor communis digitorum profundus 

 perforans. (M. perforans, Soemm. M. cubito- 

 phalangettien commun, Chauss.) arises tendi- 

 nous from the front of the ulna immediately 

 below the insertion of the brachialis anticus 

 into the tubercle of that bone, and from the 

 same as low down as the pronator quadratus ; 

 also from the interosseous ligament. It becomes 

 tendinous on its anterior face about the middle 

 of the fore-arm, thus presenting a smooth and 

 polished surface to the muscles in front of it : 

 like the superficial flexor, it forms its four 

 tendons, which, after traversing the palm of 

 the hand and piercing the split tendons of the 

 superficial flexor, are ultimately inserted into 

 the third phalanx of each of the fingers. 



This muscle has the flexor longus pollicis 

 to its outer side ; the flexor carpi ulnaris to its 

 innei ; and the flexor carpi radialis, flexor com- 

 munis digitorum sublimis and palmaris longus, 

 anterior to it. 



To flex the fingers on the hand, commencing 

 with the flexion of the last phalanx on the 

 others, and the whole hand on the fore-arm, 

 constitutes the principal action of this muscle. 



3. Pronator quadratus, Scemm. (Cubito- 

 radial, Chauss.) This muscle, entirely covered 

 by those mentioned above, presents a beauti- 

 ful appearance on their removal, from the ten- 

 dinous surface admitting by its transparency 



the colour of the muscle to shine, as it were, 

 through it. 



It arises from the ulna about an inch and a 

 half above the wrist-joint, occupying exactly 

 that extent of the surface of the bone with its 

 attachments : it is inserted fleshy into the lower 

 part of the radius. 



This muscle, simple as its action appears, 

 that of rolling the radius over the ulna, per- 

 forms a most important part in those easy mo- 

 tions of the hand which the artist uncon- 

 sciously produces when he is engaged sketching 

 in bold and flowing lines the subject of his 

 picture. 



To the surgeon a knowledge of the attach- 

 ments of this muscle is peculiarly important, 

 for in those cases in which the radius is frac- 

 tured near its lower extremity it draws the 

 injured bone into the field of the flexor tendons, 

 and by bringing it into close contact with the 

 ulna, produces a deformity which great care 

 will alone obviate. 



Posterior antibrachial region. If we now 

 look to the posterior part of the fore-arm, we shall 

 find that though it may be divided into radial 

 and ulnar sections like the anterior, the propor- 

 tions between them will be very different ; for one- 

 fifth of the transverse diameter of the arm alone 

 can be correctly allotted to the radial region in 

 the upper part, and two-fifths close to the wrist- 

 joint. The line of demarcation between these 

 two regions is accurately formed in the dissected 

 arm by the radial edge of the extensor com- 

 munis digitorum. This muscle, like those on 

 the anterior surface of the arm, is wide and 

 muscular above, tendinous and comparatively 

 narrow below ; and hence we find the radial 

 section wider below than it is above. In the 

 ulnar section, we have the extensor communis 

 digitorum to the outer side ; in contact with 

 this muscle, on its ulnar side, is the extensor 

 carpi ulnaris. This muscle, at its origin at 

 the upper part of the arm, is narrow, and the 

 space, thus yielded as it were by its form, is 

 occupied by the anconeus, which forms the 

 boundary of this region on the ulnar side. 

 The space left at the lower part of the arm, 

 from the divergence of the tendons of the 

 extensor carpi ulnaris and extensor communis 

 digitorum, permits a view of the indicator. 

 The radial section contains at its upper part 

 solely the extensor carpi radialis brevior ; but 

 at the upper part of the middle of the arm, we 

 have sliding into it from behind the extensor 

 communis digitorum, the extensor ossis meta- 

 carpi pollicis, and extensor primi internodii 

 pollicis. These pursue their course obliquely 

 across the radial section till they reach the outer 

 edge of the arm. Lower down than these 

 muscles and scarcely in contact with their 

 inferior edges, we discover the tendon of the 

 extensor secundi internodii pollicis likewise 

 emerging from beneath the extensor communis 

 digitorum. 



a. Superficial muscles of the posterior anti- 

 brachial region. 1. Anconeus (epicondylo- 

 cubital, Chauss.) though usually described as 

 a distinct muscle, is, in reality, a continuation 



