ANATOMY IN A NUTSHELL. 105 



Its articular branch is given off from one of the branches to the Supinator 

 longus, Extensor carpi radians longior, or Brachialis anticus to the elbow-joint. 

 Its cutaneous branches supply the integumenl of the arm over the musculo- 

 spiral groove; in the forearm over the radial aspect of the dorsum of the forearm 

 as far as the wrist. The internal cutaneous branch given off in the axilla crosses 

 the tendon of the Latissimus dorsi, then passes behind the intercosto-humeral 

 nerve, pierces the dee]) fascia to supply the integument on the middle of the 

 back of the arm nearly to the olecranon. Ii gives off its upper and lower ex- 

 ternal cutaneous before it pierces the external intermuscular septum; the upper 

 one perforates the outer head of the Triceps, accompanies the cephalic vein to 

 the elbow and supplies the integument over the lower half of the outer and inner 

 aspect of the arm. The lower one is the larger. It arises behind the external 

 condyle to simply the integument on the lower part of the arm and radial as- 

 pect of posterior surface of forearm as far as the wrist. It anastomoses with 

 the musculo-spiral and internal cutaneous. 



The radial nerve is the smaller of the two terminal branches of the musculo- 

 spiral and is purely cutaneous. It runs towards the wrist under the Supinator 

 longus. It passes in front of the elbow. radial recurrent a., and Supinator bre vis. 

 In the middle third of the forearm it lies parallel to. and on the outer side of. 

 the radial artery, superficial to the Pronator radii teres muscle. The nerve 

 turns backward beneath the tendon of the Supinator longus and becomes cu- 

 taneous by piercing the deep fascia of the outer side of the forearm about three 

 inches from its distal extremity: here it divides into two branches, external 

 and internal. The externa! one supplies the integument on ball and outer 

 border of thumb, anastomosing with the musculo-cutaneous. The inner one 

 anastomoses with the musculo-cutaneous and dorsal branch of the ulnar, sup- 

 plying integument on the dorsum of the hand and fingers in a manner somewhat 

 similar to that of the median nerve on the palmar surface, the first branch to 

 the inner side of the thumb, the second to the radial side of the index finger, 

 the third to the adjacent sides of the index and middle fingers, and the fourth 

 to the adjacent sides of the middle and ring fingers. 



The posterior-interovseous nerve passes around the outer side of the prox- 

 imal end of the radius, through the substance of the Supinator brevis to the 

 back of the forearm, then passe> between the superficial and deep layers to 

 about the middle of the forearm where it passes beneath the Extensor longus 

 pollicis to lie on the interosseous membrane on which it passes almosl to the 

 wrisl in company with the posterior interosseous artery. At the the distal ex- 

 tremity it accompanies the terminal branch of the anterior interosseous artery. 

 It then passes through the rourth opening of the posterior annular ligament to 

 the back of the wrist where it has a ganglion upon it. from which are given oft 

 its branches of distribution to the wrist-joint and carpal joint.-. It supplies all 

 the muscles on the back of the forearm excepl the Anconeus. It supplies nine 

 muscles in all. viz., Extensor communis digitorum, Extensor minimi digiti, 

 Extensor carpi ulnaris, Supinator brevis, Extensor ossis metacarpi pollicis, 

 Extensor longus pollicis, Extensor brevis pollicis, Extensor indicis, all ol which 



