516 VEN^ CXYM. X 



chamber formed by the separation of the lamina of the medias- 

 tinum when they join the first rib on each side. 



From this part of the curve three large branches go off, 

 namely, one, which soon divides into the carotid and the sub- 

 clavian arteries of the right side ; a second, somewhat smaller, 

 which is the left carotid ; and a third, which is the left subclavian 

 artery. 



When the heart and its great vessels are viewed from be- 

 hind, (after they have all been filled with injection ; and the 

 pericardium, mediastinum, and windpipe have been removed,) 

 the aorta appears first, descending behind the other vessels; the 

 pulmonary artery then appears, dividing so as to form an obtuse 

 angle with its two great branches, each of which divides again 

 before it enters the lung to which it is destined. 



Under the main trunk of the pulmonary artery is the left 

 auricle : its posterior surface is nearly of a square form, and 

 each of the pulmonary veins proceeds from one of its angles. 

 These veins ramify in the substance of the lungs, at a very 

 short distance from the auricle : the two uppermost of them are 

 situated rather anterior to the branches of the pulmonary 

 artery. 



In this posterior view, the pulmonary vessels of the right side 

 cover a great part of the right auricle, as it is anterior to them. 

 The lower portion of the auricle, with the termination of the 

 inferior cava, is to be seen below them. Above them the supe- 

 rior cava appears ; and in that part of it which is immediately 

 above the right branch of the pulmonary artery, is the orifice of 

 the vena azygos. 



In its natural situation in the thorax, the superior cava is 

 connected by cellular membrane to the right lamen of the 

 mediastinum, and is supported by it. At a small distance 

 below the upper edge of the sternum, it receives the trunk 

 formed by the left subclavian and internal jugular vein, which 

 passes obliquely across the sternum below its inner edge, in the 

 upper space between the lamina of the mediastinum. 



