400 HEALTH AND DISEASE 



inferior branch of the sixth cervical nerve, and the levator also receives 

 a slight contribution from the seventh. 



Radial or Musculo-Spiral Nerve. This nerve derives its fibres 

 from the seventh and eighth cervical pairs, and also from the first dorsal 

 root. It is the largest of the branches furnished by the brachial plexus. 

 From its point of origin it passes downwards, crossing over the inferior 

 part of the subscapularis and the teres major muscles. It then dips down 

 and takes an outward course under the great head of the triceps, winding 

 round the humerus in the musculo-spiral groove to gain the front of the 

 elbow-joint, where it is found beneath the extensor metacarpi and extensor 

 pedis muscles. In its course it gives branches to the great and small 

 heads of the triceps, and to the scapulo-ulnaris muscles, the caput medium, 

 and anconeus. 



Its terminal branches are destined to the extensor metacarpi magnus, 

 flexor metacarpi externus, the flexor pedis, extensor os suffraginis, and skin. 



Median Nerve. The median nerve is formed by the union of two 

 branches: one comes from the sixth, seventh, and eighth cervical, the other 

 from the eighth cervical and the first dorsal. It passes down the limb 

 at first in front of the humeral artery, and continues its downward course 

 in company with the posterior radial artery until a short distance above 

 the knee. Here it divides, the inner branch forming the internal plantar 

 nerve, the outer uniting with the ulnar to form the external plantar nerve. 

 Its branches are distributed to 1, the superficial pectoral; 2, a consider- 

 able branch which passes between the coraco-humeralis, to which it gives 

 fibres, and expends itself in the biceps; 3, a branch which leaves the parent 

 trunk at the middle of the humerus, goes to the brachialis anticus, and 

 sends off a branch to the skin of the forearm; 4, to the flexor metacarpi 

 internus and the flexor pedis perforans and perforatus. 



The Ulnar Nerve. This nerve is chiefly derived from the dorsal 

 roots of the brachial plexus. It is less considerable in size than the one 

 just described. Placed behind the humeral artery, it dips down beneath 

 the scapulo-ulnaris, between it and the caput parvum, to reach the 

 posterior part of the inner condyle of the humerus. From this point it 

 proceeds to the back of the forearm, and following the posterior border of 

 the ulnaris accessorius, terminates by joining a branch of the median just 

 above the knee. It assists in forming the external plantar nerve, and 

 gives some twigs to the front of the carpus. The branches given off in 

 its downward course supply the superficial pectoral muscle, the skin of 

 the forearm, and, excepting the external and internal flexors of the meta- 

 carpus, all the muscles behind the radius. 



Subcutaneous Thoracic Nerve. A long slender nerve situated 



