THE THORAX AS A WHOLE 81 



and the, transverse about 4 inches (10 cm.). The 

 parts which pass through the upper opening are, 

 from before backward in or near the middle line the 

 sternohyoid and sternothyroid muscles, the remains 

 of the thymus gland, the trachea (windpipe), the 

 esophagus (gullet), thoracic duct, inferior thyroid 

 veins, longus colli muscle of each side, bloodvessels 

 and nerves. 



The inferior or lower opening is formed by the twelfth 

 thoracic vertebra behind, by the twelfth ribs at the 

 sides, and in front by the eleventh, tenth, ninth, 

 eighth, and seventh costal cartilages, which ascend 

 on either side to form the subcostal angle, from the 

 apex of which the ensiform cartilage projects. The 

 lower opening is wider transversely than from before 

 backward. It slopes obliquely downward and back- 

 ward, so that the cavity of the thorax is much deeper 

 behind than in front. The diaphragm closes in the 

 opening forming the floor of the thorax, and has passing 

 through it the inferior vena cava, the esophagus, 

 and vagi nerves, the aorta, thoracic duct, vena azygos 

 major, and sometimes splanchnic nerves. 



The thorax contains the lungs and their pleurae, 

 the heart and its pericardium, the aorta and branches, 

 and the structures mentioned under the upper opening, 

 which pass through it. 



The female thorax differs from the male as follows: 

 general capacity is less, sternum is shorter, the upper 

 margin of the sternum is on a level with the lower 

 part of the body of the third thoracic vertebra (in the 

 male it is the body of the second thoracic vertebra), 

 the upper ribs are more movable, and thus allow a 

 greater expansion of the upper part of the thorax than 

 in the male (Gray) . 



The Sternum or Breast Bone. This is a flat, narrow 



bone, situated in the median line of the front of the 



chest, and in the adult consists of three portions. It 



is likened to an ancient sword; the upper piece, 



6 



