160 



THE VOYAGE OF H.M.S. CHALLENGER. 



(c) Two branches also pass off to supply the first and second heads of the triceps 

 hrachii (5). 



After giving off the nerve to the pectoralis major, the large cord of the plexus divides 

 into two branches, of which one is distributed to the palmar or concave, and the other to 



the dorsal or convex surface of the wing. 



The Palmar Branch. 



The branch to the concave surface of the wing (6) accompanies the arteruil rete 

 mirabile across the internal surface of the humerus, and divides about the middle in length 

 of that bone into two branches, which may be named the radial and ulnar. 



Fig. 1. — Diagram of the Brachial Plexus of Eudyytes chrysocome. 



(A) The Radial Nerve (7) passes as far as the elbow, where it divides into two 

 branches. 



(i.) Tlie first of these (8) extends downwards along the anterior border of the radius as 

 far as the wrist joint, beyond which I could not trace it, but apparently it becomes cutaneous 

 in that region. From this branch a twig is given off to supply the brachiaHs internus 

 muscle. 



(ii.) The second branch of the radial nerve (9) extends along the concave surface of the 

 wing, lying in the interval between the radius and ulna, and in close relation to the muscles 

 occupying tbat space. It crosses the wrist joint, and extends as far as the radial metacarpal 

 bone, where it is distributed to the shin. 



