fs — 
THE PERICARDIUM. 749 
cases, with the inner ends of the cartilages of the fourth, fifth, and sixth ribs of the 
left side. Its posterior surface forms the anterior boundary of the posterior media- 
stinum; it is in relation with the cesophagus and the descending aorta, both of 
which it separates from the back of the left auricle. Each lateral aspect is in close 
contact with the mediastinal portion of the parietal pleura, the phrenic nerve and 
its accompanying vessels intervening. The inner surface of the fibrous sac is led 
by the serous pericardium, which is closely attached to it. 
The serous pericardium is a closed sac containing a little fluid (liquor peri- 
cardi). It is surrounded by the fibrous pericardium and invaginated by the heart. 
It is, therefore, separable into two portions—the parietal, which lines the inner sur- 
face of the fibrous sac, and the visceral, which ensheaths, or partially ensheaths, the 
Left phrenic nerve 
Left vagus nerve 
_ Aorta 
Left pulmonary artery 
Aorta—— 
Left bronchus 
Pulmonary artery. 
—> Left pulmonary veins in root of 
we lung 
Superior vena cava 
Right pulmon- _ 
ary veins ~Left pulmonary veins 
Pericardium ; 1 
Pericardium 
Inferior vena _ 
cava 
Diaphragm 
Fic. 551.—Poster1or WALL OF THE PERICARDIUM AFTER REMOVAL OF THE Heart, showing the relation of 
the serous pericardium to the great vessels. From a formalin preparation made by Professor Birmingham. 
heart and the great vessels; but the two portions are, of course, continuous with 
each other where the serous layer is reflected on to the great vessels as they pierce 
the fibrous layer. The majority of the great vessels receive only partial coverings 
from the visceral layer: thus the superior vena cava is covered in front and 
laterally ; the pulmonary veins in front, above, and below; and the inferior vena 
cava, for a very short distance, in front and laterally. The aorta and the 
pulmonary artery are enclosed together in a complete sheath of the visceral layer ; 
and when the pericardial sac is opened from the front it 1s possible to pass 
the fingers behind them and in front of the auricles, from the right to the left 
side, through a passage called the great transverse sinus of the pericardium. The 
spaces or pouches which intervene between the vessels which receive partial coverings 
from the serous pericardium are also called sinuses ; and the largest of them, which 
ia 
