1090 



THE KESPIKATOEY SYSTEM. 



great arteries which spring from it ; (2) the innominate veins and part of the ven 

 cava superior; (3) the trachea, oesophagus, and thoracic duct; (4) the phrenic 

 vagi, and cardiac nerves, and the left recurrent nerve ; (5) the thymus. 



The middle mediastinum is the wide part of the area which contains th 

 pericardium, and lies below the superior mediastinum. In addition to th 

 pericardium and its contents the middle mediastinum contains the phrenic nerve 

 and their accompanying vessels. 



The ventral mediastinum is that part of the interpleural region which lies betwee: 

 the pericardium dorsally and the body of the sternum ventrally. In its superio 



--.-.Spinal medulla 



7777"- " 



Trachea 



_ _ , - - (Esoph agus 

 _---4th thoracic vertebra 

 ^,-' Innominate artery 

 .-Left common carotid 

 -Left innominate vein 



Manubrium sterni 



__Synchondrosis 

 "sternal is 



Right pulmonary 

 artery 



----- Pericardial cavity 



Aortic valve 

 - Body of sternum 



. Right atrio- 

 ventricular valve 



| .Wall of right 

 ,jl ventricle 



T| (Esophagus 



Diaphragm 

 Descending aorta 



Xiphoid process 



-Liver 



FIG. 867. SAGITTAL SECTION THROUGH THE THORAX OF AN OLD MAN. The superior border of the 

 manubrium sterni and the bifurcation of the trachea are lower than in the average adult 



part this region can hardly be said to exist, seeing that there the two pleura 

 sacs come into contact with each other on the ventral aspect of the pericardium 

 but below the level of the sternal ends of the fourth costal cartilages the lef 

 pleura falls short of the right pleura, and an interval is apparent. The only content 

 to be noticed in the ventral mediastinum are a few lymph glands and some areola 

 tissue, in which ramify some lymph vessels, and some minute twigs from th 

 internal mammary artery. 



The dorsal mediastinum is that part of the interpleural region which 

 situated dorsal to the pericardium. It may be regarded as an inferior continua 

 tion of the more dorsal part of the superior mediastinum, and many of th 

 structures in the one are prolonged into the other. The arbitrary superior limi 

 of the dorsal mediastinum is the inferior border of the fourth thoracic vertebr; 

 Ventrally it is bounded by the pericardium and the vertical part of th 

 diaphragm. Dorsally it is limited by the bodies of the last eight thoracic vertebr. 

 and 07i each lateral side by the mediastinal pleura. It contains the descendin 



