THE THORAX. 319 



the arm, and the posterior, outer surface of the forearm 

 nearly to the elbow. The posterior interosseous nerve sup- 

 plies the extensor carpi radialis brevior, supinator brevis, 

 extensor communis digitorum, extensor minimi digiti, ex- 

 tensor carpi ulnaris, extensor metacarpi pollicis, extensor 

 indicis, extensor brevis, and longus pollicis muscles. The 

 intercostohumeral nerve, after entering into a plexi- 

 form arrangement with the lesser internal cutaneous and 

 cutaneous branch of the third intercostal nerve at the floor 

 of the axilla, continues outward, downward, and sends some 

 filaments posteriorly to supply the integument of the upper 

 posterior part of the arm and axilla, over the latissimus 

 dorsi muscle. 



The nerves receive their filaments from the following 

 sources : 



The suprascapular and subclavius 5, 6, 7. * 



The external anterior thoracic, 5, 6, 7. 



Musculocutaneous, 5, 6, 7. 



The internal anterior thoracic, 8, i. 



Lesser internal cutaneous and internal cutaneous, 8, I. 



Ulnar, (7), 8, I. 



Subscapular, circumflex, and musculospiral, 5, 6, 7, 8. 



The median, 5, 6, 7, 8, I. 



THE THORAX. 



For the landmarks see page 255. 



The dissection of the soft parts anterior to the ribs has been already per- 

 formed, and their description given in the preceding pages. 



Remove the sternum and costal cartilages by cutting through the latter as 

 close to the ribs as possible (when the ribs are not needed, the division had 



* Numerals refer to the number of the cervical and dorsal nerves forming 

 the brachial plexus. 



