PRONATOR RADII TERES— FLEXOR CARPI RADIALIS 313 



1. PRONATOR RADII TERES 



The pronator radii teres — named from its aetion and somewhat cylindrical 

 shape — is a thick rihljon-shaped muscle. 



Origin. — First head : (1) by the common tendon from the front of the internal 

 condyle; and (2j from the lowest part of the internal condylar ridge; (3) from tlie 

 deep fascia covering it, and the internmscular septum which separates it from the 

 flexor carpi radialis and the flexor sublimis digitorum. 



Second head : from the inner border of the coronoid process. 



Insertion, — The rough impression on the middle of the outer surface of the 

 radius. 



Structure. — The higher of the two heads, which is much the larger, arises 

 partly l)y a short tendon, and partly by muscular filn-es, and is separated from the 

 lower head by a small tendinous arch through which passes the median nerve. 

 The lower head, which lies concealed by the rest of the muscle, arises by a small 

 aponeurotic band. The thick fleshy muscle passes obliquely doAvnwards and out- 

 wards across the front of the forearm. Below the middle of its anterior surface 

 begins the tendon of insertion, which expands and covers the whole of the muscle 

 for a short distance before it is inserted by a strong fibrous band into the special 

 impression for it upon the most prominent portion of the outward curve of the 

 raclius. 



Nerve-supply. — From the outer and inner cords of the brachial plexus 

 (through the sixth cervical nerve) by means of filaments derived from the median 

 nerve just before it passes through the arch between the two heads. These fila- 

 ments enter the muscle at its deep surface a short distance above the middle of its 

 outer border. 



Action. — (1) To pronate the forearm. In supination, the tendon is to some 

 extent wrapi)ed round the radius, as the tendon of the biceps is in pronation. In 

 contraction, the muscle so to speak, unwraps itself and so causes the radius to 

 revolve around the axis, which passes through the middle of its head and the lower 

 end of the ulna. Its insertion into the convexity of the curve of the radius places 

 the line of the muscle as far as possible from this axis, and so gives it some 

 mechanical advantage. On the other hand, the obliquity of its insertion diminishes 

 the power of the muscle, and is one of the causes which make pronation a more 

 feeble movement than supination. (2) It will also assist in the flexion of the 

 forearm. 



Relations. — Superficially, the bicipital and deep fasciae and superficial veins, 

 the radial vessels and nerve, and, lower down, the brachio-radialis (supinator 

 longus) and radial extensors. Deeply, the brachialis anticus, flexor sublimis digi- 

 torum, supinator brevis, and the median nerve. By its outer border, it forms the 

 inner boundary of the space at the bend of the elbow, and by its inner border it is 

 in contact with the flexor carpi radialis. 



Variations. — The pronator radii teres frequently extends at its origin for some distance further 

 up the internal condylar ridge. It may also receive a separate head from the internal inter- 

 muscular septum, the inner border of the humerus, or an abnormal supracondylar process ; some- 

 times also from the biceps or brachialis anticus. This third head bridges over the brachial artery 

 and median nerve. 



2. FLEXOR CARPI RADIALIS 



The flexor carpi radialis — named from its action as a flexor of the wrist and 

 its position on the radial side of the joint — is flat and fusiform. 



Origin. — (1) The common tendon from the front of the internal condyle; (2) 

 the deep fascia and the intermuscular sejita whicli lie Ix'tween the muscle and the 

 ])ronator radii teres, the flexor sublimis digitorum, and the palmaris longus. 



Insertion. — The front of the Ijase of the second metacarpal bone; and usually 

 by a smaller slip into that of the third as well. 



Structure. — Its fleshy fibres are contained in an ajioneurotic case which forms 

 an elongated four-sided pyramid, the apex lieing at the internal condyle, and the 



