920 THE NERVOUS SYSTEM 



The scaieni and longus colli (figs. 675, 678) are supplied by twigs which arise from 

 the lower three or four cervical nerves immediately after their exit from the inter- 

 vertebral foramina. 



The lateral branches of the infra-clavicular portion are the anterior thoracic 

 nerves (external and internal), from the outer and inner cords respectively, the 

 medial antibrachial (internal) cutaneous and the medial brachial (lesser internal) 

 cutaneous nerves, from the inner cord, and the subscapular nerves and thoraco-dorsal 

 from the posterior cord. 



The external anterior thoracic nerve arises from the outer cord of the plexus 

 and contains fibres from the fifth, sixth, and seventh nerves (figs. 675, 678, 679). 

 After communicating with the internal anterior thoracic it pierces the coraco-clavicu- 

 lar fascia and ends in branches that supply the pectoralis major muscle. The internal 

 anterior thoracic nerve arises from the inner cord (figs. 675, 678, 679), contains 

 fibres from the eighth cervical and first thoracic nerves, and passes forwards between 

 the first stage of the axillary artery and the axillary vein. It unites with a branch 

 from the external anterior thoracic, to form a loop which is placed in front of the 

 first stage of the axillary artery; it gives branches to the pectoralis minor, and 

 branches which pass through the latter muscle and end in the pectoralis major. 

 From the loop additional branches are furnished to the pectoralis major. 



The Medial Brachial (Lesser Internal) Cutaneous Nerve, or nerve of Wris- 

 berg (fig. 678) , arises from the inner cord of the brachial plexus and sometimes con- 

 tains fibres from the eighth cervical and first thoracic nerves, but usually fibres from 

 the first thoracic nerve alone. It runs downwards on the inner side of the axillary vein, 

 being separated by that vessel from the ulnar nerve, and it continues downwards 

 with a slight inclination dorsalwards under cover of the deep fascia on the inner side 

 of the arm. At the middle of the arm it pierces the deep fascia, and near the bend 

 of the elbow it turns somewhat sharply dorsalwards to supply the integument which 

 covers the olecranon process (fig. 680). As it traverses the axilla the nerve of Wris- 

 berg communicates with the intercosto-brachial nerve, forming one, or sometimes 

 two loops (fig. 678). In its course down the arm it gives a few fine twigs to the in- 

 tegument. This nerve may be absent, its place being taken by the intercosto-' 

 brachial or by part of the posterior brachial (internal) cutaneous branch of the radial 

 (musculo-spiral) or, rarely, by a branch from the first intercostal nerve. 



The Medial Antibrachial (Internal) Cutaneous Nerve (figs. 675 and 678) arises 

 from the inner cord immediately above the ulnar nerve. It contains fibres from the 

 eighth cervical and first thoracic nerves. At its origin it lies directly on the inner 

 side of the axillary artery (fig. 679), but it soon becomes more superficial and then 

 lies in the groove between the artery and the vein. In the upper two-thirds of the 

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



At the junction of the middle and lower thirds of the arm this nerve pierces the 

 deep fascia, in company with the basilic vein, and divides into an anterior and a poste- 

 rior branch. Previous to its division it gives off twigs which pierce the deep fascia . 

 and supply the integument of the upper and inner part of the arm. The volar 

 (anterior) branch is larger than the ulnar (posterior) ; it passes in front of or behind 

 the median basilic vein, and divides into several twigs which run down the forearm, 

 supplying the integument covering its anterior and internal aspect as far as the 

 wrist, and anastomosing with the branches of the ulnar nerve. The ulnar (posterior) 

 branch passes downwards and dorsalwards in front of the internal condyle of the 

 humerus, and divides into branches which supply the skin on the postero-internal 

 aspect of the forearm. It anastomoses with the dorsal antibrachial (inferior external) 

 cutaneous branch of the radial (musculo-spiral) nerve and the dorsal branch of the 

 ulnar nerve. 



The Subscapular Nerves are branches of the posterior cord (fig. 678). They are 

 three in number, are distinguished as upper, thoraco-dorsal or middle, and lower, and 

 are distributed to the subscapularis, latissimus dorsi, and teres major muscles. 



The upper or short subscapular nerve is derived from the fifth and sixth cervical 

 nerves. It lies in the upper and posterior part of the axillary fossa, and it is distri- 

 buted exclusively to the subscapularis muscle. It is occasionally double. 



The thoraco-dorsal, middle, or long subscapular nerve consists mainly of fibres 

 from the seventh and eighth cervical nerves, but it may contain fibres from the 

 fifth or the sixth nerve. It passes behind the axillary artery, accompanies the 



