THE RADIAL REGION. 483 



similar to those for the other flexor tendons, is inserted into the base of the 

 last phalanx of the thumb. 



Relations. By its superficial surface, with the Flexor sublimis digitorum, 

 Flexor carpi radialis, Supinator longus, and radial vessels ; by its deep surface, 

 with the radius, interosseous membrane, and Pronator quadratus ; by its ulnar 

 IxH-'b-i'. with the Flexor profundus digitorum, from which it is separated by the 

 anterior interosseous vessels and nerve. 



The Pronator quadratus is a small, flat, quadrilateral muscle, extending trans- 

 versely across the front of the radius and ulna, above their carpal extremities. It 

 arises from the oblique or pronator ridge on the lower part of the anterior surface 

 of the shaft of the ulna ; from the lower fourth of the anterior surface and the 

 anterior border of the ulna ; and from a strong aponeurosis which covers the inner 

 third of the muscle. The 'fibres pass horizontally outward, to be inserted into 

 the lower fourth of the anterior surface anxl anterior border of the shaft of the 

 radius. 



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

 Flexor longus pollicis. Flexor carpi radialis, and the radial vessels ; by its deep 

 9urfaee 4 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 sup- 

 plies the Flexor longus pollicis and Pronator quadratus. 



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

 Pronator radii teres helps to rotate the radius upon the ulna, rendering the hand 

 prone : when the radius is fixed it assists the other muscles in flexing the 

 forearm. The Flexor carpi radialis is one of the flexors of the wrist ; when 

 acting alone it flexes the wrist, inclining it to the radial side. It can also 

 r in pronating the forearm and hand, and, by continuing its action, to bend 

 the elbow. The Flexor carpi ulnaris is one of the flexors of the wrist : when 

 acting alone it flexes the wrist, inclining it to the ulnar side, and, by continuing 

 to contract, to bend the elbow. The Palmaris longus is a tensor of the palmar 

 fascia. It also assists in flexing the wrist and elbow. The Flexor sublimis 

 digitorum flexes the second phalanges. It assists in flexing the wrist and elbow. 

 The Flexor profundus digitorum flexes the terminal phalanges (see page 497). 

 After the Flexor sublimis 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. 



Radial Region (Fig. 308). 



Supinator longus. Extensor carpi radialis longior. 



Extensor carpi radialis brevier. 



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 thuse structures. The muscles will then be exposed. The removal of the fascia will 

 be considerably facilitated by detaching it from below upward. 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 



