362 PRACTICAL ANATOMY. 



and to all the muscles in the radial region, and also to all the muscles on the pos- 

 terior part of the foramen. Its cutaneous branches are as follows : (i) Radial, to 

 the integument of the ball of the thumb and to three and one-half ringers dorsally, 

 as far as the base of the distal phalanx (Fig. 242) ; (2) internal cutaneous branches 

 to the skin on the inner and posterior part of the arm ; (3) external cutaneous 

 branches to the skin on the outer and front part of the arm. (Fig. 241.) The 

 articular branch to the shoulder is sometimes taken with the circumflex. The 

 posterior nerve-cord is composed of both the circumflex and musculo-spiral and 

 other branches. 



6. Name tJic muscles arising from the external condylar ridge. 

 The brachio-radialis and extensor carpi radialis longior. 



7. Give the origin, course, and distribution of the posterior interosseons nerve. 

 A branch of the musculo-spiral ; it passes between the upper and deep layers 



of the supinator brevis muscle. It lies between the deep and superficial groups 

 of posterior forearm muscles, which it supplies. Note that the musculo-spiral 

 nerve gives off branches to the radial group of muscles prior to its division into 

 the radial and posterior interosseous. Demonstrate this on your dissection. 



If you have not already done so, review you dissection of the musculo- 

 spiral nerve and show that the branches that supply the humeral heads of the 

 triceps muscle are given off at the back of the humerus ; that branches are given 

 off in the axilla to the scapular head. This nerve sometimes accompanies the 

 ulnar nerve as a long slim branch, known as the ulnar collateral. 



8. Describe tlie dorsal inter ossei muscles. 



They are four in number. They are supplied by the ulnar nerve. They 

 have origin from the contiguous sides of the metacarpal bones. (Fig. 248.) 

 Their single independent action is abduction of the fingers, which is always 

 associated physiologically with supination of the radius. Their synergistic action 

 is with the palmar interossei and lumbricales to produce metacarpo-phalangeal 

 flexion, and extension of the second and third phalanges. They are inserted 

 into the bases of three fingers, as shown in figure 248. 



1. Describe tJie median nerve. 



It arises by two heads an outer and an inner from the outer and inner 

 cords of the brachial plexus respectively. (Fig. 42.) It accompanies the axillary 

 artery and its prolongation, the brachial, to the elbow. It gets into the forearm 

 by passing between the condylar and coronoid heads of the pronator radii tores 

 muscle. It gives off no branches to the flexor muscles of the forearm. It is, in 

 rare cases, fused with the musculo-cutaneous nerve. It is said to give off two 

 articular branches to the elbow-joint. It supplies all the muscles on the anterior 

 surface of the forearm, except the flexor carpi ulnaris, and one-half of the flexor 

 profundus digitorum. It supplies three and one-half fingers with sensation. 

 In the hand it supplies the two radial lumbricales and all the muscles of the 

 thenar eminence, except the adductor pollicis and one head of the flexor brevis 

 pollicis. It is accompanied by an artery below the elbow. Sometimes this artery 

 is as large as the radial. It passes under the anterior annular ligament. In the 

 forearm the median nerve lies in the sheath of the flexor sublimis digitorum, on 

 the posterior surface of this muscle. The digital branches of this nerve supply 

 the finger-joints. 



2. Describe tlic itlnar nerrc. 



It is a branch of the inner cord of the brachial plexus. It is attended by the 

 inferior profunda artery above the elbow, and by the ulnar below. It gains the 

 forearm by passing between the two heads olecranon and condylar of the 

 flexor carpi ulnaris. It supplies the flexor carpi ulnaris, and the ulnar half of 

 the flexor profundus digitorum. It supplies one and one-half fingers dorsally 

 and paltnarly. It supplies in the hand all the muscles not innervated by the 



