THE THORAX . 47 



ARTICULATIONS OF THE THORAX 







Sternum. The three pieces (manubrium, body, and xiphoid 

 appendix) are connected together by fibro-cartilages and anterior 

 and posterior ligaments. After middle life they become united in 

 one bone. 



Ribs (costa).* The costal cartilages are connected in front to 

 the sternum, or to each other, as already mentioned. The heads 

 articulate with the bodies of two thoracic vertebrae. (Exceptions: 

 the first, eleventh, and twelfth are each connected to one body.) 

 Where the neck of the rib joins the shaft (marked by a tubercle) 

 it rests against the tip of the transverse process of a vertebra behind 



Head of rib 



Articular surface of 

 transverse process 



Inter-articular liga- 

 ment 



FIG. 42. HEADS OF Rms ARTICULATING WITH TWO VERTEBRAE. (After Morris.) 



it, which thus forms a brace for it. All of these joints are enclosed 

 by capsules and lined with synovial membrane, providing for the 

 movements of the ribs in breathing, talking, etc. (Figs. 40, 42.) 



Vertebrae.- Their joints have been described. 



By the articulation of the ribs with the spine at the back and 

 the sternum in front, the bony thorax is completed. It is shaped 

 like a cone, flattened before and behind, and shortest in front 

 (the sternum reaching only as low as the ninth dorsal vertebra). 

 The intervals between the ribs are called the intercostal spaces. 



The elasticity of the ribs and cartilages and their gliding joints 

 give a yielding character to the thoracic walls to accommodate the 

 movements of the lungs within. 



