THORACIC AND ABDOMINAL VISCERA 365 



the fifth and sixth ribs, half way between the sternum and the 

 nipple line. 



The mammary gland covers the front part of .the spaces from 

 the third to the fifth ribs. It lies between layers of the superficial 

 fascia in front of the pectoralis major muscle. 



The superior opening transmits the trachea, esophagus, and 

 important vessels and nerves. The floor (or diaphragm) has three 

 openings one for the passage of the aorta and thoracic duct, one 

 for the inferior vena cava, and one for the esophagus and vagus 

 nerves. 



The thoracic viscera are the esophagus, trachea and bronchi, 

 lungs, and heart. The esophagus lies close to the spinal column, 

 and the trachea is in front of the esophagus, dividing into the large 

 bronchi, whose branches are the bronchial tubes. The heart and 

 large vessels are in the anterior and middle part of the thoracic 

 cavity (Fig. 234). 



The heart is wrapped in the pericardium, and each lung is 

 wrapped in a pleural sac which is placed between the lung and the 

 chest wall. An incision through that part of the wall which is 

 bounded by the ribs would pierce the costal pleura and open the 

 pleural cavity. A wound of the lung would injure the pulmonary 

 pleura. 



The large nerves in the thoracic cavity are the vagi, lying close 

 to the esophagus, the sympathetic, whose branches form cardiac 

 and pulmonary plexus, and the two phrenic nerves, right and left, 

 running down on either side of the pericardium to the diaphragm. 



The mediastinum is the space between the lungs. In it all of 

 the thoracic viscera except the lungs are situated. 



THE ABDOMEN, ABDOMINAL VISCERA, AND PERITONEUM 



The boundaries of the completed abdomen are the spinal 

 column and quadratus lumborum muscles at the back, the hip-bones 

 below, the rectus muscles in front, and the broad fiat muscles at the 

 side. The diaphragm is its roof. The transversalis fascia lines the 

 cavity, and the peritoneum is within the fascia, held to it by areolar 

 tissue called subperitoneal or subserous tissue. 



On the anterior surface of the abdomen observe the outline 

 made by the lower ribs, between the thorax and abdomen, the two 

 sides meeting in the subcostal angle just below the sternum. The 



