CHAPTER XV. 



MEDIASTINUM. 



ANATOMY AND DESCRIPTION OF CONTENTS. 

 ARTERIES. TRACHEA. 



LANDMARKS. OESOPHAGUS. 



VEINS. THORACIC DUCT. 



LANDMARKS. NERVES. 



STRUCTURES OPPOSITE FOURTH DORSAL VERT. 



The mediastinum is the space in the middle of the 

 chest formed by the non-approximation of the pleurae. 

 This space is bounded, in front, by the sternum; behind, 

 by the vertebrae ; laterally, by the pleurae, and contains all 

 of the thoracic structures with the exception of the lungs 

 and pleurae. When the chest of a subject is opened and 

 the lungs removed, the mediastinum is readily appreciated 

 and is seen to form a pyramidal-shaped column with a 

 base, about five inches in breadth, resting on the dia- 

 phragm, and an apex, about three inches wide, corre- 

 sponding to the thoracic inlet. About an inch below the 

 inlet, i.e., about opposite the middle of the manubrium, 

 the mediastinal column is contracted, so as to measure 

 only about one and a half inches from side to side. The 

 measurements of the upper opening of the thorax are, on 

 an average, about five inches transversely and about two 

 and a half inches from before backwards, and, since the 

 width of the apex of the mediastinum is about three inch- 

 es, the remaining two inches of the transverse diameter of 

 the inlet are occupied by the apices of the lungs. The 

 mediastinal column is divided into two parts by an ima- 

 ginary plane which passes through it at the upper limit of 

 the pericardium, and which corresponds to the junction 

 of the manubrium and the gladiolus, anteriorly, and, to 



