THE ROOT OF THE LUNG. 4 



at the inner surface, about midway between the base and apex, 

 and about a third of the way from the posterior to the anterior 

 border of the lung. 



In front of the root 011 both sides are the phrenic and the relations, 

 anterior pulmonary plexus of nerves, the phrenic nerve being some 

 little distance from it upon the side of the pericardium. Anterior 

 to the root of the right lung also is the superior vena cava. 

 Behind on both sides is the posterior pulmonary plexus ; and on 

 the left side there is, in addition, the descending aorta. Above, 

 on the right side, is the great azygos vein ; and on the left side, the 

 arch of the aorta. Below each root is the fold of pleura called the 

 ligamentum latum pulmonis. 



In the root of the lung are collected a branch of the pulmonary consti- 

 artery, two pulmonary veins, and a division of the air tube 

 (bronchus), as well as small nutritive bronchial arteries and veins, 

 and some nerves and lymphatics. The large vessels and the air 

 tube have the following positions to one another : 



On both sides the bronchus is on a posterior plane, and the their reia. 

 pulmonary veins are lowest down on the most anterior plane, and 

 the pulmonary artery is intermediate. On the right side the 

 uppermost branch of the bronchus occupies the highest place" 

 and the remainder of the bronchus is directed downwards and 

 outwards behind the blood vessels, the pulmonary artery is next 

 highest and the veins are lowest down. On the left side the differences 

 pulmonary artery occupies the highest place with the veins below 

 it, within its concavity, and being anterior to the artery at their 

 emergence from the lung ; the bronchus is directed downwards and 

 outwards behind tL and is intermediate in level. This 



difference in the two sides is accounted for by the fact that the 

 bronchus of the right side gives off its branch to the upper lobe of 

 the lung before it is crossed by the artery ; while on the left side 

 there is no corresponding branch of the airtube, and the artery 

 crosses the undivided bronchial stem. 



THE PERICARDIUM. 



The bag containing the heart is named the pericardium. It is Pericar. 

 situate in the middle of the thorax, in the interval between the lum ' 

 two pleura?. 



Dissection. The surface of the pericardium should now be Clean ves- 

 cleaned, and the student should dissect out the large vessels above Sel3ofheart * 

 the heart, and trace the nerves (fig. 161, p. 444). 



In cleaning the fibrous pericardium it will be noticed that bands 

 connect it with the back of the upper and lower portions of the 

 sternum still remaining the superior and inferior sterno-pericardial 

 ligaments. 



The large artery curving to the left al >ove the pericardium is the First aorta, 

 aorta, which furnishes three trunks to the head and the upper 

 liml>s, viz., from right to left, the innominate, the left common 



D.A. G G 



