THE THORAX. 263 
(d) The trachea divides at its posterior end into two portions, the 
(e) 
(f) 
right and left bronchi, one for each lung. Each bronchus 
is again divided into smaller portions, the bronchial rami, 
which penetrate the substance of the organ and redivide into 
smaller tubes. On the right side a small eparterial 
bronchus is given off from the right bronchus. It passes 
to the superior lobe of this side, and lies in front of the right 
pulmonary artery. 
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. 
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 may 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) 
(b) 
(c) 
The oesophagus. It traverses the thorax in a median posi- 
tion, entering the diaphragm at the hiatus oesophageus. 
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. 185). 
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. 
