178 Anatomy of thk Rabbit. 



(e) The branches of the pulmonary artery and the pulmonary- 

 veins may be traced for a short distance on the medial por- 

 tion, or hilus, of each organ. 



(f) The vagus nerve passes to the dorsal side of the bronchus, 

 giving off a number of branches, which accompany the 

 bronchus to the lung. 



The lungs may be removed, together with a portion of the trachea, 

 care being taken to leave the vagus nerves in place. The lungs mav 

 then be examined to better advantage, and the surface also prepared for 

 the next dissection. 



5. The following structures may now be traced on the dorsal wall of 

 the thorax: 



(a) The oesophagus. It traverses the thorax in a median posi- 

 tion, entering the diaphragm at the hiatus oesophageus. 



(b) The vagus nerves. The right and left nerves pass backward 

 along the lateral walls of the oesophagus, and are connected 

 with one another through nerve plexuses lying on its dorsal 

 and ventral surfaces. The left cord is that appearing at the 

 posterior end of the oesophagus in a ventral position and 

 passing to the ventral surface of the stomach. The right 

 cord occupies a corresponding dorsal position and passes to 

 the dorsal surface of the stomach (p. 119). 



(c) The thoracic aorta (aorta thoracalis) passes backward on the 

 ventral surface of the vertebral column, leaving the thorax 

 through the hiatus aorticus, the latter being the aperture 

 enclosed by the crura of the diaphragm. Its branches in the 

 thorax are the intercostal arteries (aa. intercostales), beginning 

 with the fourth, which are given off metamerically in the 

 intercostal spaces, and pass laterad to the thoracic wall. 



(d) The thoracic portions of the sympathetic trunks lie on the 

 lateral surfaces of the bodies of the thoracic vertebrae. The 

 posterior ganglia give origin to the splanchnic nerve, the 

 latter passing backward into the abdominal cavity (p. 118). 



(e) The levatores costarum; a series of small muscles arising 

 from the transverse processes of the vertebrae and the heads 

 of the ribs and inserted on the anterior margins of the next 

 succeeding ribs. 



(f) The intercostal nerves (nn. intercostales) accompany the 

 intercostal arteries to the lateral wall of the thorax. 



(g) The azygos vein (v. azygos) is a small, asymmetrical, venous 

 trunk lying to the right of the dorsal surface of the aorta. 

 It receives the majority of the intercostal veins, which 

 accompany the corresponding arteries and nerves, the 

 tributaries extending backward to the first lumbar veins. 

 It opens forward into the right superior caval. The more 

 anterior intercostal veins are tributaries of the right and left 

 supreme intercostal veins which open into the corresponding 

 superior cavals. 



