77//1 THORAX. 



203 







2. The origin of the stcrno-liyoid muscle. 

 3 . The origin of tJie sterno-tJiyroid muscle. 



4. The origin and insertion of the triangnlaris stcrni. 



5. The costal and sternal origins of t/te diapJiragm. 



6. The parietal layer of the pleura, through which you can see the muscles. 



7. The internal mammary artery and veins, on each side of the sternum, 

 giving off their anterior intercostal and other arteries. (Fig. 143.) 8 



Dissection. Cut through the ribs in the mid-axillary line. (Fig. 145.) Cut 

 through the abdominal walls along the margin of the false ribs. Cut through 



PHRENIC NERVE 



Subclavian artery 

 Subclavian vein, cut 



Anterior intercostal branch 



Anterior intercostal branch 



Mnsculo-phrenic artery 



Deep circumflex iliac artery - 



Common carotid artery 



Internal jugular vein 

 Subclarian rein, cut 

 Soaleuus anticus muscle 



Trianpcularis aterni muscle 

 Perforating branch 



Superior epigastric artery 



Deep epigastric artery 



FIG. 143. SCHEME OF THE INTKRNAI. MAMMARY ARTERY. 



the diaphragm close to the ribs and sternum. Then elevate from below 

 the section of thoracic wall you have made loose. As you turn this section up 

 you will see a large amount of anterior mediastinal connective tissue behind the 

 sternum. Elevate the section slowly ; let an assistant divide the connective 

 tissue, and do not injure the numerous structures that enter or leave the apex 

 of the thorax. 



Figure 141 shows the infracostales. These muscles arise near the angle of 

 the ribs, from the inner surface and lower border ; they are inserted into the 

 second rib above. They are also called snbcostals. 



