RADIAL REGION. 



389 



of the forearm. Its outer side 

 is crossed obliquely by the ex- 

 tensor tendons of the thumb. 

 By its deep surface, with the 

 elbow-joint, the Extensor Carpi 

 Radialis Brevior, and back part 

 of the wrist. 



The Extensor Carpi Radialis 

 Brevior is shorter, as its name 

 implies, and thicker than the pre- 

 ceding muscle, beneath which 

 it is placed. It arises from the 

 external condyle of the hume- 

 rus by a tendon common to it 

 and the three following muscles; 

 from the external lateral liga- 

 ment of the elbow-joint ; from 

 a strong aponeurosis which 

 covers its surface; and from 

 the intermuscular septa between 

 it and the adjacent muscles. 

 The fibres terminate about the 

 middle of the forearm in a flat 

 tendon, which is closely con- 

 nected with , that of the pre- 

 ceding muscle, accompanies it 

 to the wrist, lying in the same 

 groove on the posterior surface 

 of the radius ; passes beneath 

 the annular ligament, and, di- 

 verging somewhat from its fel- 

 low, is inserted into the base 

 of the metacarpal bone of the 

 middle finger, on its radial 

 side. 



The tendons of the two pre- 

 ceding muscles pass through 

 the same compartment of the 

 annular ligament, and are lu- 

 bricated by a single synovial 

 membrane, but are separated 

 from each other by a small ver- 

 tical ridge of bone, as they lie 

 in the groove at the back of 

 the radius. 



Relations. By its superficial 

 surface, with the Extensor Carpi 

 Radialis Longior, and with the 

 extensor muscles of the thumb 

 which cross it. By its deep 

 surface, with the Supinator 

 Brevis, tendon of the Pronator 

 Radii Teres, radius, and wrist- 

 joint. By its ulnar border, with 

 the Extensor Communis Digi- 

 torum. 



Fig. 241. Posterior Surface of Forearm. 

 Superficial Muscles. 



