DISSECTION OF THE UPPER EXTREMITY 67 



branches carefully and follow them to their terminations, com- 

 paring their behavior with the text-book descriptions. Deal simi- 

 larly with the axillary vein and its tributaries. 



Subclavius Muscle (M. subclavius). 



Clean it. Examine its form, position, origin, insertion, action, 

 and innervation. 



With a small hand-saw excise the middle third of the clavicle. 

 Eeflect the M. subclavius. 



Brachial Plexus (Plexus brachialis). (Fig. 17.) 



Divide the M. pectoralis minor four centimetres from the 

 coracoid process and reflect the two portions lateralward and 

 medialward respectively, avoiding injury to the medial anterior 

 thoracic nerve. Examine the continuity of the axillary artery 

 and vein with the subclavian artery and vein. Ligature the ar- 

 tery in two places at level of clavicle and cut between. Cut vein 

 similarly. Turn axillary vessels downward. Clean thoroughly 

 the nerves making up the brachial plexus. Study carefully the 

 formation of the plexus, using the cadaver before you, Tra- 

 mond's models, and text-book descriptions. Does the plexus in 

 your cadaver differ from the type ordinarily described? If so, 

 how? Make a careful drawing of the plexus in your subject, 

 with its various branches, labelling each neatly. Note that the 

 plexus can be divided into a supraclavicular portion (pars 

 supraclavicularis) and an infraclavicular portion (pars infra- 

 clavicularis) . All the short branches are counted as belonging 

 to the former, even though they do not actually come off until 

 the trunks are below the clavicle. 



In conjunction with the dissector of the head and neck, study 

 the 



Pars supraclavicularis. 



(a) Posterior thoracic nerves (Nn. thoracales posteriores). 



(aa) Dorsal nerve of scapula (N. dorsalis scapulae) (0. T. nerve 



to rhomboids). 



(ab) Long thoracic nerve (N. thoracalis longus) (0. T. external 



respiratory nerve of Bell). 



(b) Anterior thoracic nerves (Nn. thoracales anteriores). 



(ba) Lateral (0. T. external). 



(bb) Medial (0. T. internal). 



(c) Subclavian nerve (N. subclavius). 



(d) Suprascapular nerve (N. suprascapularis) . 



(e) Subscapular nerves (Nn. subscapulares) . 



(f) Thoracodorsal nerve (N. thoracodorsalis) (0. T. middle or long 



subscapular) . 



(g) Axillary nerve (N. axillaris) (0. T. circumflex). 



