

THE THORAX 



117 



It is conical in shape, being narrow above and broad below, flattened from before 

 backward, and longer behind than in front. It is somewhat reniform on trans- 

 verse section on account of the projection of the vertebral bodies into the cavity. 



First thoracic 





FIG. 113. The thorax from behind. (Spalteholz.) 



Boundaries. The posterior surface is formed by the twelve thoracic vertebrae 

 and the posterior parts of the ribs. It is convex from above downward, and pre- 

 sents on either side of the middle line a deep groove, in consequence of the lateral 

 and backward direction which the ribs take from their vertebral extremities to 

 their angles. The anterior surface, formed by the sternum and costal cartilages, 

 is flattened or slightly convex, and inclined from above downward and forward. 

 The lateral surfaces are convex; they are formed by the ribs, separated from 

 each other by the intercostal spaces, eleven in number, which are occupied by 

 the Intercostal muscles and membranes. 



The upper opening of the thorax is reniform in shape, being broader from side 

 to side than from before backward. It is formed by the first thoracic vertebra 

 behind, the upper margin of the sternum in front, and the first rib on either side. 



