388 MUSCLES AND FASCIA. 



Relations. By its anterior surface, with the Flexor Profundus Digitorum, the 

 Flexor Longus Pollicis, Flexor Carpi Eadialis, and the radial vessels. By its 

 posterior 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 by the median, through its branch, the anterior interosseous nerve, 

 which also supplies the Flexor Longus Pollicis and Pronator Quadratus. 



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

 acting on the forearm, are the Pronator Eadii Teres and Pronator Quadratus, 

 which rotate the radius upon the ulna, rendering the hand prone; when prona- 

 tion has been fully effected, the Pronator Eadii Teres assists the other muscles 

 in flexing the forearm. The flexors of the wrist are the Flexor Carpi Ulnaris 

 and Flexor Carpi Eadialis; and the flexors of the phalanges are the Flexor 

 Sublimis and Flexor Profundus Digitorum; the former flexing the second pha- 

 langes, and the latter the last. The Flexor Longus Pollicis flexes the last 

 phalanx of the thumb. The three latter muscles, after flexing the phalanges, 

 by continuing their action, act upon the wrist, assisting the ordinary flexors of 

 this joint ; and all those which are attached to the humerus 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 EEGION. (Fig. 241.) 



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, 

 remove all those structures. The muscles will then 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, which cross obliquely the larger 

 tendons running down the back of the radius. 



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

 the forearm. It is 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-spinal 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 

 fetacarpi Pollicis and the Extensor Primi Internodii Pollicis. By its deep 

 surface, with the humerus, the Extensor Carpi Eadialis Longior and Brevior, 

 the insertion of the Pronator Eadii 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 Lonyior 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 Eadialis Brevior im- 

 mediately behind the styloid process; and is inserted into the base of the 

 metacarpal bone of the index finger, on its radial side. 



Relations. By its superficial surface, with the Supinator Longus, and fascia 



