THE THORAX. 



205 



3. An anterior uw//, formed by the sternum and cartilages of the ribs, \\itli 

 their investing soft parts. ( )n this we find the internal mammary arteries and 

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



4. A posterior isn't, 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. 7'ii'M lateral uw//.v, formed by the ribs and intercostal spares, between the 

 angles and the costo-chondral articulations. 



Vena card superior 



Arch cf aorta 



BRONCHUS 



1'tilinonarii artery 

 }*ulmonary vein 



ENSIFORM CARTILAGE 



I'M;. 144. ANTERIOR VIKW 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, ligamenta 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 nie,iiastiiitil portion, or non-hmg-coTitaining compartment. 



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



