THE THORAX. 



179 



The serratus anterior (magnus) muscle (Fig. 202) passes from the side of 

 the chest to the vertebral or posterior border of the scapula, arising by nine or ten 

 digitations from the eight or nine upper ribs, the second having two. The slip arising 

 from the sixth rib is the one most prominently seen on raising the arm away from 

 the side, it passes the farthest forward. The slips into the fifth, seventh, and eighth 

 ribs may also be seen. This muscle passes across the axilla from in front backward, 



Trapeziu 



Deltoid 



Infraspinatu 



Teres mino: 

 Teres major 



Sternomastoid 



plenius 



Levator (anguli) scapulae 

 Scalenus medius 



Latissimus dorsi 



External oblique 

 Internal obliqu 



Petit's triangle 



FIG. 203. Muscles of the back. 



lying on the chest-wall. It is supplied by the posterior thoracic nerve from the 

 fifth, sixth, and seventh cervicals. This nerve is also called the long external 

 respiratory nerve of Bell. The internal respiratory nerve is the phrenic, which comes 

 from the third, fourth, and fifth cervical nerves. One of the main functions of this 

 muscle is to keep the scapula applied to the chest and to aid in rotating it in elevation 



