6 THE SUPERIOR EXTREMITY 



Referred pain occurs in the shoulder region in diaphragm- 

 atic pleurisy and, on the right side, in tropical abscess of 

 the liver and, more rarely, in pathological conditions of the 

 gall-bladder. The stimuli reach the fourth cervical segment 

 via the phrenic nerve (p. 242). 



Anteriorly, as already mentioned, the skin is supplied entirely 

 by C. 3 and C. 4, but the skin of the corresponding area on the 

 dorsal aspect is supplied by the fourth to the sixth cervical and 

 the upper three thoracic nerves (Fig. 3). From this it will 

 be seen why, in fracture dislocations below the fourth cervical 

 vertebra, the line of anaesthesia is higher on the posterior than 

 on the anterior aspect of the body. 



Below the shoulder, i.e. over the floor of the axilla, the skin 

 is supplied by the lateral cutaneous branches of the second 

 (intercosto-brachial, p. 32) and third intercostal nerves. 



Superficial Veins. The cephalic vein runs upwards in the 

 groove between the deltoid and the pectoralis major, and passes 

 backwards through the superficial infra-clavicular triangle to 

 join the axillary vein. It frequently communicates with the 

 external jugular by means of a small vein which crosses in 

 front of the clavicle (Fig. 35). This vessel becomes considerably 

 enlarged in those cases of excision of the breast in which a 

 portion of the axillary vein has been excised, as it offers an 

 efficient channel for the return of venous blood from the 

 upper limb. 



Trapezius. The origin of this muscle extends from the 

 occipital bone above to the lowest thoracic spine. The upper 

 fibres are attached to the posterior border of the clavicle in its 

 lateral half. They support the clavicle, and, through it, part 

 of the weight of the upper limb, and are supplied by the (spinal) 

 accessory nerve. When the nerve is injured, the shoulder on 

 the affected side falls to a lower level, as it has lost its muscular 

 support. The lower part of the muscle is inserted into the 

 medial border of the acromion and the upper border of the spine 

 of the scapula ; and it is supplied by the cervical plexus (C. 3 

 and 4). A bursa is situated between the muscle and the flattened 

 root of the scapular spine. When the whole muscle contracts, 

 the point of the shoulder is elevated particularly by the upper 

 fibres and it is owing to this movement that abduction of the 

 arm is possible beyond an angle of 90. 



Sterno-Clavicular Joint. The line of the joint passes 

 from above downwards and laterally. The articular surface of 



