310 DISSECTION OF THE THORAX. 



The root of the, lung consists of the vessels entering the fissure on the 

 inner surface ; and as these are bound together by the pleura and some 

 areolar tissue they form a foot-stalk, which fixes the lung to the heart and 

 the windpipe. The root is situate at the inner surface, about midway be- 

 tween the base and apex, and about a third of the breadth from the poste- 

 rior border of the lung. 



In front of the root on both sides, are the phrenic and the anterior pul- 

 monary nerves, the former being at some little distance from it ; and an- 

 terior to the right root is the descending cava. Behind on both sides, is 

 the posterior pulmonic plexus ; and on the left side there is, in addition, 

 the descending aorta. Above on the right side is the vena azygos ; and 

 on the left side, the arch of the aorta. Below each root is the fold of 

 pleura called ligamentum latum pulmonis. 



In the root of the lung are collected a branch of the pulmonary artery, 

 two pulmonary veins, and a division of the air tube (bronchus) ; small 

 nutritive bronchial arteries and veins, and some nerves and lymphatics. 

 The large vessels and the air tube have the following position to one 

 another : 



On both sides the bronchus is most posterior, the pulmonary veins most 

 anterior, and the pulmonary artery between the other two. In the direc- 

 tion from above down the position on the right side is, bronchus, pulmo- 

 nary artery, and pulmonary veins ; but on the left side the bronchus and 

 artery have changed places, consequently the relative position will there 

 be artery, bronchus, and veins. This ditference in the two sides may be 

 accounted for by the left branch of the air tube being at a lower level 



than the right. 



THE PERICARDIUM. 



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

 in the middle of the thorax, in the interval between the pleura of opposite 

 sides. 



Dissection. Supposing the surface of the pericardium to be already 

 cleaned, the student should next dissect out the large vessels connected 

 with the heart, and the nerves. 



The large artery curving to the left above the heart is the aorta, which 

 furnishes three trunks to the head and the upper limbs, viz., innominate 

 to the right, next left common carotid, and left subclavian. On its left 

 side lies the pulmonary artery. 



Above the arch of the aorta a large venous trunk, left innominate, 

 crosses over the three before said arteries, and ends by uniting on the right 

 side with the right innominate vein in the upper cava. Several small 

 veins, which may be mistaken for nerves, ascend over the aorta, and enter 

 this trunk. Define the branches of this vein, and especially one crossing 

 the aortic arch towards the left side, which is the left superior intercostal 

 vein. 



The large vein by the side of the aorta which enters the top of the heart 

 is the upper cava : look for the azygos vein opening into it behind. 



Seek the following nerves of the left side which cross the arch of the 

 aorta: The nerve most to the left, and the largest, is the vagus ; the 

 next largest in size on the right of the vagus is the phrenic. Between 

 the preceding nerves, and close to the coats of the artery, are the two 

 following, the left superficial cardial nerve of the sympathetic, and the 



