Clinical Anatomy of the European Hamster 
To date, only benign tumors have been induced, 
with some spontaneous tumors observed in this 
organ. 
The tracheobronchial lymph nodes {Inn. trache- 
obronchiales) consist of eight to ten nodes, of which 
the smaller are found in the ventral mediastinum. 
There are three right ventral bronchial lymph 
nodes located lateral to the thymus gland on the 
right side of the trachea. They drain the heart, 
esophagus and trachea and empty into the right 
lymphatic duct {ductus lymphaticus dexter), which 
empties into the right jugular vein. There are also 
three left ventral bronchial lymph nodes lateral to 
the trachea and directly ventral to the bifurcation. 
They drain the left lungs and empty into the thor- 
acic trunk {truncus thoracicus) which opens into the 
left brachiocephalic vein (Fig. 4-24). 
4.4.2.1.4 Nerves 
The right vagus nerve {n. vagus dexter) (Figs. 
3-11, 4-17) enters the thoracic cavity to the right of 
the right common carotid artery. There it veers 
dorsally and extends along the right side of the 
esophagus throughout the thoracic cavity. The left 
vagus nerve {n. vagus sinister) (Figs. 3-11, 4-17) 
runs dorsally along the left common carotid, dorsal 
to the left external jugular vein and left cranial vena 
cava, and crosses between the left common carotid 
and the left subclavian arteries, ventral to the aortic 
arch, running in the serosa ventral to the root of the 
left lung. Here it gives rise to a branch, the left re- 
current laryngeal nerve {n. laryngeus recurrens 
sinister), which wraps around the aortic arch and 
runs cranially up the left side of the trachea to the 
laryngeal muscles. The right recurrent nerve (n. 
laryngeus recurrens dexter) originates from the 
right vagus nerve at the level of the base of the 
heart. It wraps around the truncus costocervicalis 
and runs cranially up the right side of the trachea to 
the laryngeal muscles. Caudal to the aortic arch, the 
left vagus turns toward the surface of the left cranial 
vena cava, where it is found just dorsal to the tho- 
racic aorta. It then runs along the left side of the 
esophagus, which it accompanies into the abdomi- 
nal cavity. In addition to the vagus nerves, the 
thoracic cavity also houses the paired phrenic 
nerves (nn. phrenici) originating from the brachial 
plexus. The right phrenic nerve enters the thoracic 
cavity dorsal to the right subclavian vein and pro- 
ceeds dorsally along the right cranial vena cava to 
the right auricle of the heart, continuing left of the 
caudal vena cava to the central diaphragmatic ten- 
don. The left phrenic nerve runs along the left side 
of the cranial vena cava and lies dorsal to the left 
ventricle of the heart and ventral to the esophagus. 
It runs with the esophagus to the diaphragm where 
it divides into several smaller branches. The brach- 
ial plexus {plexus brachialis) is composed of the 
large ventral branches of the fifth to eighth cervical 
and first thoracic nerves. Only by very careful prep- 
aration can two additional fine ventral branches be 
recognized under magnification. These come from 
either the fourth cervical or second thoracic nerves. 
The nerves from the brachial plexus wrap around 
the first rib and approach the shoulder ventral to 
the middle scalene muscle. 
4.4.2.2 The Dorsal Mediastinum 
The dorsal mediastinum lies behind the frontal 
plane passing in front of the tracheal bifurcation 
and the dorsal surface of the pericardium, running 
parallel with the vertebral column. It is an irregur 
larly shaped space extending caudally beyond the 
pericardium, due to the slope of the diaphragm. The 
pericardium is its ventral border and the vertebral 
column from the second to the eleventh thoracic 
vertebrae is the dorsal boundary. The mediastinal 
pleurae are the lateral limits and the diaphragm is 
the caudal boundary. Meshed in abundant alveolar 
tissue, its structures include the thoracic part of the 
descending aorta, the azygos vein, the vagus and 
phrenic nerves, the tracheal bifurcation with the 
two main bronchi and lung roots, the esophagus, 
thoracic duct and clusters of large lymph nodes. 
4.4.2.2.1 Lymphatic Tissue 
The dorsal mediastinum includes the largest of 
the tracheobronchial lymph nodes. The two right 
dorsal bronchial nodes are found adjacent to the 
laterocranial wall of the right main bronchus at the 
level of the tracheal bifurcation. These nodes drain 
the right lung and heart and empty into the right 
lymphatic duct. The left dorsal bronchial lymph 
node is located at the level of the tracheal bifurcation 
and adjacent to the aortic arch. It drains the left 
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