THE UPPER LIMB 357 



radii brevis. Here it divides into branches which come into 

 relation with the musculo-spiral nerve and its terminal divisions. 

 Most of these are distributed to the muscles arising from the ex- 

 ternal epicondyle, and they anastomose with the posterior inter- 

 osseous recurrent. One branch, however, ascends with the musculo- 

 spiral nerve between the brachio-radialis and brachialis anticus, 

 and anastomoses with the anterior terminal branch of the superior 

 profunda of the brachial. The radial recurrent also gives articular 

 twigs to the elbow-joint. 



The muscular branches arise at frequent intervals along the forearm. 



The anterior radial carpal artery, of small size, arises from the 

 inner side of the radial at the level of the lower border of the pro- 

 nator quadratus, along which it passes inwards, lying deeply beneath 

 the flexor tendons. At the middle hne it anastomoses with the an- 

 terior ulnar carpal artery to form the anterior carpal arch. This 

 arch is reinforced from above by the anterior branch of the anterior 

 interosseous artery, and from below by the recurrent branches of the 

 deep palmar arch. In this manner the anterior carpal arch is con- 

 verted into a rete, the branches of which are distributed to the wrist - 

 joint, and the carpal articulations and bones. 



The superficial volar artery arises either below the preceding, or 

 sometimes above it. It passes downwards over, or through, the 

 thenar muscles, in which, if of small size, it terminates. When 

 large, it reaches the palm, and anastomoses with the ulnar artery 

 to complete the superficial palmar arch. 



Varieties of the First Part.— (i) The artery may arise high up from the 

 brachial, or axillary. (2) When of high origin, it may descend superficial to 

 the semilunar fascia of the biceps and deep fascia of the forearm. (3) The 

 I artery may turn backwards over the brachio-radialis just below the centre 

 jof the forearm. (4) It may be joined by a vas aberrans from the brachial, 

 jor axillary. (5) It may terminate at the lower part of the forearm, its dis- 

 itribution being taken up by the ulnar, median, or anterior interosseous. 



1 The second and third parts of the radial artery will be afterwards 



I described. 



Radial Venae Comites. — ^The radial artery is accompanied by two 



; venae comites, which are placed one on either side of the vessel, and 



I they communicate at frequent intervals by transverse branches 



jing upon it. They terminate above by uniting to form the 



external brachial vena comes. 



Radial Nerve. — ^The radial nerve is one of the terminal branches 

 of the musculo-spiral, its fibres being derived from the sixth cervical, 

 -ind sometimes from the fifth and seventh. It passes straight down- 

 kvards under cover of the brachio-radialis, lying at first a little to 

 ithe outer side of the radial artery, then getting closer to it at the 

 l:entre of the forearm, and finally leaving the vessel in the lower 

 bart by turning backwards beneath the tendon of the brachio- 

 ladialis on its way to its cutaneous distribution, which has been 

 iilready described. It is a sensory nerve, and gives ofE no branches 

 kntil it reaches the back of the limb. 



