58 



DISSECTION OF THE DOG 



to its bifurcation, where the oesophagus, inclining towards the right, 

 intervenes. 



Of the bronchi, the right is the larger and is in contact with the vena 

 azygos; the left bronchus is crossed dorsally by the oesophagus. 



N. vagus. — The right and left vagus nerves descend the neck in intimate 

 association with the right and left sympathetic nerve cords, and enter the 

 thorax between the innominate vein and subclavian artery of their own side. 

 The close relationship of the vagus and sympathetic nerves ceases within the 

 first rib or the first intercostal space. 



Trachea 



Bronchus sinister 

 Lobus apicalis 



Lobus cardiaciis - "" 

 Lobus diaphragmaticus .-- 



Bronchus dexter 



- Lobus apicalis 

 --Lobus cardiacus 

 Lobus diaphragmaticus 



Lobus intermedins 



Fig. 22. — Diagram of the branches of the bronchi, indicating to which lobes of the 

 lungs they are distributed. 



In the precardial and cardial mediastina the two vagus nerves have different 

 relations. The right nerve is at first lateral to the trachea. It then passes 

 within the vena azygos and across the dorsal aspect of the root of the right 

 lung, and thus reaches the oesophagus. The left nerve arrives at the oesophagus 

 by crossing the lateral face of the aorta obliquely and the dorsal aspect of the 

 root of the left lung. 



On the gullet each vagus nerve divides into a dorsal and a ventral branch 

 (ramus dorsalis et ramus ventralis). The ventral branches of the right and 

 left nerves unite just beyond the base of the heart, and form the ventral (esopha- 

 geal trunk (truncus oesophageus ventralis). The dorsal branches similarly join 

 to form the dorsal oesophageal trunk (truncus oesophageus dorsalis) , but do not 

 do so until they arrive close to the diaphragm. The two oesophageal nerve 

 trunks leave the thorax by accompanying the oesophagus through the diaphragm. 



