UPPER EXTREMITY AND THORAX, POSTERIOR. 365 



and inward, and to rotate the humerus inward (adduction, 

 extension, and internal rotation of humerus). 



The insertion being the fixed point, the muscle will raise 

 the body and swing it forward (if both muscles are acting) 

 or to one side (if only one muscle acts). Acting upon the 

 ribs, it will raise them and act as an accessory muscle of 

 inspiration. 



DISSECTION. 



Cut the deltoid away from its origin and turn it downward and forward ; in 

 doing so save its nerve and arterial supply. 



Disarticulate the clavicle from its acromial attachment ; divide the coraco- 

 clavicular ligaments and draw the clavicle out of the way. 



Remove the supra- and infraclavicular fasciae and clean the muscles covered 

 by them. Also, clean the levator anguli scapulae, rhomboid, and teres 

 muscles. Remove the fascia covering the triceps. 



The superficial fascia of the arm has been already de- 

 scribed (see page 282). 



The cutaneous nerves of the back of the shoulder and 

 arm. 



The shoulder receives filaments through the acromial 

 nerves from the third and fourth cervical nerves. See page 

 91. 



The deltoid region of the arm and a small surface of the 

 outer part of the arm from the deltoid half-way to the elbow 

 is supplied by the circumflex nerve. 



The rest of the outer portion of the arm is supplied by 

 the superior external cutaneous branch of the musculo- 

 spiral nerve. 



The inner half of the back of the arm is supplied from 

 above downward by the internal cutaneous branch of the 

 musculospiral, the intercostohumeral, and the lesser internal 

 cutaneous nerves. 



