THE UPPER EXTREMITY. 65 



Divide the pectoralis major near the middle, turn the outer portion to the insertion; reflect the inner 

 portion to the origin. Preserve the arteries, so far as possible, in connection with the main trunks. 



Pectoralis minor, 313 ; Fig. 266. (314-15-16) 



Origin. Insertion. Structure. Nerve-supply. Action. Relations. Variations. 

 Second part of the axillary artery, 552-3. (542-3) 



Relations : In front. Behind. Inner side. Outer side. 



Divide the pectoralis minor near the middle and turn to its origin and insertion. The subclavius should 

 also be divided at its insertion and thrown in toward its origin. The axillary artery will be fully 

 exposed throughout its course; its relations should be reviewed and the branches demonstrated. 

 Relations of: First part of axillary artery, 552. (S4 2 ) 



Second part of axillary artery, 552-3. (542-3) 

 Third part of axillary artery, 553. (543) 

 Chief variations in the axillary artery, 553. (543) 

 Branches of the first part of the axillary artery, 555. 

 Superior or short thoracic. 

 Acromio thoracic or thoracic axis : 



Acromial branch. Humeral branch. 

 Pectoral branch. Clavicular branch. 



Branches of the second part of the axillary artery, 555. (545) 

 Long thoracic artery. 

 Alar thoracic. 



Branches of the third part of the axillary artery, 555-6-7-8. (545-6-7-8) 

 Subscapular artery : 

 Dorsal scapular. 

 Infrascapular. 



Chief variations in the subscapular artery. 



Anterior circumflex : 



Branches : Bicipital. 

 Pectoral. 

 Chief variations. 



Posterior circumflex : 

 Branches : Nutrient. 

 Acromial. 

 Muscular. 



Chief variations in the posterior circumflex. 

 Axillary vein, 682. (668) 



Remove the middle third of the clavicle. Dissect off the fascia and connective tissue and expose the 

 nerves of origin, trunks, divisions, cords, and terminal branches of the brachial plexus. 



The brachial plexus, 832-3-4; Fig. 455. (813-14) 



The brachial plexus is formed by the anterior primary divisions of: 

 Four lower cervical nerves. 

 First thoracic nerve. 



Usually joined by communicating branches from: 

 Fourth cervical and second thoracic nerves. 

 The brachial plexus is divisible into four stages : 



First stage : All the component nerves are separate from each other. 



Four lower cervical and first thoracic nerve. 

 Second stage: Nerves unite with one another to form trunks. 



Upper trunk. Middle trunk. Lower trunk. 



Third stage: Trunks divided into three anterior and three posterior divi- 

 sions. 

 Fourth stage : Three posterior divisions unite to form posterior cord. 



Anterior divisions of upper and middle trunks unite to form 

 outer cord. 



Anterior division of inner trunk continued as inner cord. 

 Position of: The first stage of the plexus. 



Second stage. Third stage. Fourth stage. 



