310 MUSCLES AND FASCIAE. 



inner third of the muscle. The fibres pass horizontally outwards, to be inserted 

 into the lower fourth of the anterior surface and external border of the shaft of 

 the radius. 



Relations. By its anterior surface, with the Flexor profundus digitorum, the 

 Flexor longus pollicis, Flexor carpi radialis, and the radial vessels. By its poste- 

 rior surface, with the radius, ulna, and interosseous membrane. 



Nerves. All the muscles of the superficial layer are supplied by the median 

 nerve, excepting the Flexor carpi ulnaris, which is supplied by the ulnar. Of the 

 deep layer, the Flexor profundus digitorum is supplied conjointly by the ulnar 

 and anterior interosseous nerves, the Flexor longus pollicis and Pronator quadratus 

 by the anterior interosseous nerve. 



Actions. These muscles act upon the forearm, the wrist, and hand. Those 

 acting on the forearm are the Pronator radii teres and Pronator quadratus, which 

 rotate the radius upon the ulna, rendering the hand prone ; when pronation has 

 been fully effected, the Pronator radii teres assists the other muscles in flexing the 

 forearm. The flexors of the wrist are the Flexor carpi ulnaris and radialis, and 

 the flexors of the phalanges are the Flexor sublimis and Profundus digitorum ; 

 the former flexing the second phalanges, and the latter the last. The Flexor longus 

 pollicis flexes the last phalanx of the thumb. The three latter muscles, after flex- 

 ing the phalanges, by continuing their action, act upon the wrist, assisting the 

 ordinary flexors of this joint ; and all assist in flexing the forearm upon the arm. 

 The Palmaris longus is a tensor of the palmar fascia ; when this action has been, 

 fully effected, it flexes the hand upon the forearm. 



EADIAL EEGICXN". 



Supinator Longus. Extensor Carpi Eadialis Longior. 



Extensor Carpi Eadialis Brevior. 



Dissection. Divide the integument in the same manner as in the dissection of the anterior 

 brachial region ; and after having examined the cutaneous vessels and nerves and deep fascia, 

 they should be removed, when the muscles of this region will be exposed. The removal of the 

 fascia will be considerably facilitated by detaching it from below upwards. Great care should be 

 taken to avoid cutting across the tendons of the muscles of the thumb. 



The Supinator Longus is the most superficial muscle on the radial side of the 

 forearm, fleshy for the upper two-thirds of its extent, tendinous below. It arises 

 from the upper two-thirds of the external condyloid ridge of the humerus, and 

 from the external intermuscular septum, being limited above by the musculo-spiral 

 groove. The fibres terminate above the middle of the forearm in a flat tendon, 

 which is inserted into the base of the styloid process of the radius. 



Relations. By its superficial surface, with the integument and fascia for the 

 greater part of its extent; near its insertion it is crossed by the Extensor ossis 

 metacarpi pollicis and the Extensor primi internodii pollicis. By its deep surface, 

 with the humerus, the Extensor carpi radialis longior and brevior, the insertion of 

 the Pronator radii teres, and the Supinator brevis. By its inner border, above the 

 elbow, with the Brachialis anticus, the musculo-spiral nerve, and radial recurrent 

 artery ; and in the forearm, with the radial vessels and nerve. 



The Extensor Carpi Radialis Longior is placed partly beneath the preceding 

 muscle. It arises from the lower third of the external condyloid ridge of the 

 humerus, and from the external intermuscular septum. The fibres terminate at 

 the upper third of the forearm in a flat tendon, which runs along the outer border 

 of the radius, beneath the extensor tendons of the thumb ; it then passes through 

 a groove common to it and the Extensor carpi radialis brevior, immediately behind 

 the styloid process ; and is inserted into the base of the metacarpal bone of the 

 index-finger, its radial side. 



Relations^ By its superficial surface, with the Supinator longus, and fascia 

 of the forearm. Its outer side is crossed obliquely by the extensor tendons of 



