THE TJIOK.IX. 



205 



3. An anterior wall, formed by the sternum and cartilages of the ribs, with 

 their investing soft parts. On this we find the internal mammary arteries and 

 their veins, and the sterno-hyoid, sterno-thyroid, and triangularis stern i muscles. 



4. A posterior wall, formed by the thoracic portion of the vertebral column 

 and the ribs outward from their heads to the angles, with their investing soft 

 parts. 



5. Two lateral walls, formed by the ribs and intercostal spaces, between the 

 angles and the costo-chondral articulations. 



Vena cava superior 



Arch of aorta 



Pulmonary artery 



BRONCHUS 



/ 

 Pulmonary vein 



ENSIFORM CARTILAGE 



IK;. 144. ANTERIOR VIEW OK THE LUNGS: PERICARDIUM. (Modified from Bourgery.) 



The inlet or apex of the thorax is bounded by the sternum, first rib, and 

 first thoracic vertebra. The diaphragm is attached to, or rather has its origin from, 

 the sternum, ribs, hgamenta arcuata interna and externa. There are twenty- 

 four ribs, twenty-two intercostal spaces, and forty- four intercostal muscles. 



The interior of the thorax consists of: 



1. A pulmonary portion, a compartment containing the lungs. 



2. A mcdiastinal portion, or non-lung-containing compartment. 



The pulmonary portion of the thoracic cavity contains the lungs. The inner 



