THE RADIAL REGION. 



395 



digitorum flexes first the middle and 

 then the approximal phalanx. It 

 assists in flexing the wrist and elbow. 

 The Flexor profundus digitorum is one 

 of the flexors of the phalanges. After 

 the Flexor sublirnis has bent the second 

 phalanx, the Flexor profundus flexes 

 the terminal one, but it cannot do so 

 until after the contraction of the super- 

 ficial muscle. It also assists in flexing 

 the wrist. The Flexor longus pollicis 

 is a flexor of the phalanges of the 

 thumb. When the thumb is fixed it 

 also assists in flexing the wrist. The 

 Pronator quadratus helps to rotate the 

 radius upon the ulna, rendering the 

 hand prone. 



9. Radial Region (Fig. 235). 



Supinator longus. 



Extensor carpi radialis longior. 



Extensor carpi radialis 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 re- 

 moval of the fascia will be considerably 

 facilitated by detaching it from below up- 

 ward. Great care should be taken to avoid 

 cutting across the tendons of the muscles of 

 the thumb, \yhich cross obliquely the larger 

 tendons running down the back of the radius. 



The Supinator longus (brachio- 

 radialis) 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 

 supracondylar ridge of the humerus, 

 and from the external intermuscular 

 septum, being limited above by the 

 musculo-spiral groove. The fibres ter- 

 minate above the middle of the fore- 

 arm in a flat tendon, which is inserted 

 into the outer side of the base of the 

 styloid process of the radius. 



Relations. By its superficial sur- 

 face, 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 brevis 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 ; 



surface f tJe forearm> Super ' 



