PREPARATION OF THE THORAX. 501 



may be studied advantageously, after the subject has been prepared in the 

 manner now to be described. 



Take away, from each side, the five ribs which are situated between the first 

 and last true ribs, by separating their cartilages from the sternum, alfd their 

 heads from the spine ; so that the great cavities of the thorax majf be laid 

 open. 



The precise course of the mediastinum is thus rendered obvious; and the 

 sternum may now be divided with a saw throughout its whole length in the 

 same direction j so that the division of the bone may correspond with the 

 space between the lamina of the mediastinum. 



Separate the portion of the sternum cautiously, so as to avoid lacerating the 

 lamina of mediastinum ; and to keep them separate, while the trachea is 

 dissected from the neck into the cavity of the thorax ; the great transverse 

 vein and the descending cava are dissected to the pericardium ; and the left 

 carotid artery, with the right subclavian and carotid, are dissected to the curve 

 of the aorta, taking care not to destroy the lamina of the mediastinum. 



After this preparation the upper space between the lamina of the mediastinum 

 can be examined, and the relative situation of the trachea and the great 

 vessels in it can be understood. The anterior mediastinum can also be 

 studied : the root of each lung, or its connexion with the mediastinum, may 

 be seen perfectly ; and the precise situation of the lung, in its proper cavity, 

 may be well conceived. 



After this, while the portions of the sternum are separated, the pericardium 

 may be opened, and the heart brought into view : the attachment of the 

 pericardium, and to the mediastinum, and to the diaphragm, may be seen 

 with advantage in this situation. The portions of the sternum may now be 

 detached from the ribs, with which they remain connected ; and further dis- 

 section may be performed to examine the posterior mediastinum and Us con- 

 tents, and the parts which constitute the roots of the lungs. 



