1296 



HUMAN ANATOMY. 



the inner wall, lying posterior to the brachial plexus and the axillary vessels, and upon 

 the lateral aspect of the serratus magnus. It gives off successive twigs to the digita- 

 tions of the last-named muscle, which alone it supplies. The fibres derived from the 

 fifth cervical nerve supply the upper part, those from the sixth the middle and those 

 from the seventh the lower part of the muscle. 



Variations. The contribution from the fifth nerve sometimes fails to join the main nerve 

 and goes directly to its distribution to the upper digitations. The root from the seventh nerve 

 may be absent. An additional root may be contributed by the eighth cervical nerve. 



Practical Considerations. The posterior thoracic nerve may be paralyzed 

 by an injury in the suprascapular region or in the axilla, by carrying heavy 

 weights upon the shoulder, or as a result of infectious disease, cold or rheu- 

 matism. The most noticeable sign is a prominence of the scapula (winged scapula), 

 from the failure of the paralyzed serratus magnus muscle to hold the vertebral border 

 of the scapula close to the thorax. That border and the inferior angle project and 



Axillary artery 



Pectoralis minor, stump 



Outer cord of plexu 

 Coraco-brachialis 

 Musculo-cutaneous nerve 



Median ner 

 Uln 



FIG. 1093. 



Acromlal thoracic artery, 

 Deltoid 



Cephalic vein 



Int. cutaneous nei 



Pectoralis major, stump 



Biceps, 

 short head' 



Posterior cir- 

 cumflex artery 

 and a muscular 

 branch 



Lesser internal 



cutaneous nerve 

 Long thoracic artery 

 Intercosto-humeral m s.- 

 Subscapular artery 



I Jitissimus dorsl 

 Long subscapular nerve 

 Teres majoi ~~ 



Posterior thoracic nerve 



Sterno-cleido-mastoid 



lixt. anterior thoracic nerve 



-Clavicle 

 -Axillary vein 



Internal anterior 



thoracic nerve 



Pectoralis major, cut 

 ^Pectoralis minor, ci't 



Serratus magnus 

 Dissection of right axilla, showing relations of brachial plexus to blood-vessels. 



become prominent. When the arm is in front of the chest the deformity is most 

 marked and the lower angle approaches the mid-line of the back. The patient can- 

 not lift anything heavy with the affected arm. Since the incision to open an axillary 

 abscess is made vertically in the middle of the thoracic wall of the axillary space, to 

 avoid the vessels at its borders, this nerve is in some danger as it passes to the 

 serratus magnus muscle. 



4. The muscular branches supply the longus colli, the scaleni anticus, 

 medius and posticus and the subclavius. 



a. The longus colli and scalenus anticus are supplied by small twigs which arise from 

 the anterior surface of the lower four cervical nerves as they leave the vertebral column. 



b. The scaleni medius and posticus receive fibres given off from the posterior aspect of 

 the lower four cervical nerves as they pass through the intervertebral foramina. 



c. The nerve to the subclavius (n. snbclnvius) takes its origin from the outer trunk of the 

 plexus, its til MVS coming mainly from the fifth cervical nerve. It passes through the subclavian 

 triangle, over tin- third portion of the subclavian artery and behind the clavicle, to enter the 

 deep surface of the subclavius muscle. 



