790 THE yEJlVOUS SYSTEM 



vessel from the ulnar m-rve. It passes ilou invards with a slight inclination hack- 

 wards under cover of tiie deej) fascia on the inner side of the arm. At the middle 

 of the arm it i)ierces the fascia, and near the hend of the elbow it turns soniewhiit 

 sharj)ly backwards to supply the intejzunicnt ■which covers the olecranon process. 

 As it traverses the axilla the nerve of ^\'risl>erg communicates with the intercosto- 

 humeral nerve forming one or sometimes t^vo loops. In its course down tlie arm it 

 gives a few fine twigs to the integument. 



(3) The internal cutaneous is a l)rancli of the inner cord, its fibres being ulti- 

 mately derived from the eighth cervical and first thoracic nerves. At its origin it 

 lies on the inner side of the axillary artery, but it soon passes forwards and lies in 

 the groove between the artery and the vein anteriorly. In the upper two-tliirds of 

 the arm it lies in front and to the inner side of the brachial artery. 



It then pierces the deep fascia in company with the V)asilic vein, and divides 

 into an anterior and a posterior braneli. Previous to its division it gives off a twig 

 which [)ierces the deep fascia, and su])])lies tlie integument of the upi)er and inner 

 part of the arm. (a) The anterior branch is larger than the posterior, and 

 divides at acute angles into several twigs, some of Avhich pass in front of and some 

 liehind the median basilic vein, and then run down the forearm to supply the 

 integuments covering its anterior and internal aspect as far as the wrist, anasto- 

 mosing with the branches of the ulnar nerve, (b) The posterior branch passes 

 downwards and backwards in front of the internal condyle of the humerus, and 

 divides into branches which su})ply tlie skin on the postero-internal aspect of the 

 forearm. It anastomoses with the inferior external cutaneous branch of the in\is- 

 culo-spiral nerve and the dorsal brancli of tlie ulnar nerve. 



(4) The musculo-cutaneous nerve is a branch of the outer cord of the 

 brachial plexus. It is composed of fibres which are derived from the fifth, sixth, 

 and seventh cervical nerves. It is i)laced at first close to the outer side of the 

 ]>rachial artery, but soon leaves that vessel and pierces the coraco-brachialis muscle 

 in a direction olilif][uely downwai'ds and outwards. Continuing this oblique direc- 

 tion, it passes between the ])iceps and Ijrachialis anticus muscles, and becomes super- 

 ficial at the outer l^order of the former muscle, a little above the bend of the elljow. 

 It then passes on the deep surface of the median cej)halic vein, and divides into an 

 anterior and a posterior branch. Previous to its division, the musculo-cutaneous 

 nerve supplies three muscles, viz. the coracQ-hrachialis, the biceps, and the bradtlalh 

 anticus. It also supplies twigs to the humerus, the nutrient artery, and the elbow- 

 joint. The nerve to the coraco-brachialis consists of two or three twigs which 

 are given off from the nerve close to its origin, and before it has traversed the 

 muscle. In the child this branch rises separately from the seventh cen'ical nerve. 

 The nerves to the biceps and brachialis anticus muscles arise from the 

 musculo-cutaneous nerve as it is ])assing between these muscles. There is a sep- 

 arate branch for each head of the biceps. The posterior terminal branch is 

 small, and is directed downwards and liackwards in front of the external condyle 

 of the humerus to be distributed to the skin on the outer and posterior aspect of 

 the forearm as low as the wrist. It anastomoses wdth the radial nerve and Avith 

 the inferior external cutaneous branch of the nnisculo-spiral nen'c. The anterior 

 branch runs cloAvnwards on the outer and anterior part of the forearm, supplying 

 tbe integument of that region, and having communicated near the wrist with the 

 radial nerve, it sends a branch through the deep fascia Avhich accom])anies the 

 radial artery to the back of the wrist; it terminates in the skin covering the middle 

 part of tin? thenar eminence. 



(•")) The median nerve is formed by filn-es derived from the fifth, sixth, 

 seventh, and eighth cervical and first thoracic nerves. It arises by two heads, 

 one from the outer, and one from the inner cord. The inner head crosses ol)li(]uely 

 in front of tho third stage of the axillary artery, and joins the outer head on the 

 external side of that vessel. The median nerv(^ runs almost vertically down the 

 arm under cover (^f the skin and fascia, and is partially overlapped by the biceps. 

 In the upper part of the arm it is placed on the outer side of the brachial artery. 

 About the middle of the arm it crosses in front of that vessel, and then runs down 

 on the iimer side of the artery to the bend of the elbo\v. It then passes between 

 the two heads of the ])i-on;itor radii teres, and is separated from the ulnar artery in 



