468 



DISSECTION OF THE THORAX. 



relations 



Left com- 

 mon caro- 

 tid: 



relations in 

 the thorax. 



Left sub- 

 clavian 

 artery : 



course and 

 relations in 

 the chest. 



The great 

 veins are : 



Vena cava 

 superior : 



formed by 

 innominate 

 veins ; 



course ; 



relations ; 



branches. 



The artery is crossed by the left innominate vein, and lies 

 behind the upper piece of the sternum, and the origins of the 

 sterno-hyoid and sterno-thyroid muscles. At first it rests on the 

 trachea, but as it ascends it is placed on the right side of the air- 

 tube. To its right is the innominate vein of the same side. Usually 

 no lateral branch arises from this artery. 



LEFT COMMON CAROTID ARTERY. The common carotid artery 

 of the left side of the neck is longer than the right by the distance 

 between the arch and the top of the sternum. 



In the thorax the artery ascends obliquely to the left sterno- 

 clavicular articulation, but not so close as the innominate to the 

 first piece of the sternum and the origin of the depressor muscles 

 of the hyoid bone and larynx. In this course it passes beneath 

 the left innominate vein, and the remains of the thymus gland. 

 At first it lies on the trachea, but afterwards inclines to the left 

 of that tube, so as to be placed over the oesophagus and the thoracic 

 duct. To its outer side is the left vagus, with one or more cardiac 

 branches of the sympathetic nerve. 



The LEFT SUBCLAVIAN ARTERY ascends to the neck through the 

 upper aperture of the thorax, and then curves outwards between the 

 scaleni, where it has the same relations as the vessel of the right side. 



The trunk is directed almost vertically from the arch of the 

 aorta to the level of the first rib. In the thorax it is deeply placed, 

 near the spine. To its inner side is at first the trachea, and after- 

 wards the oesophagus with the thoracic duct. On its outer side it 

 is invested by the left pleura, and in the hardened specimen its 

 position is represented by a shallow groove in the lung, in which 

 it rests. The left innominate vein crosses in front of the vessel as 

 it enters the neck. Somewhat anterior to the artery, though 

 running in the same direction, are some of the cardiac nerves. 



VEINS. In addition to the cardiac veins, there are the superior 

 and inferior cavae, and the pulmonary veins ; the former are the 

 great systemic vessels which return impure blood to the right auricle 

 of the heart ; and the latter convey pure blood from the lungs to 

 the left auricle. 



The SUPERIOR or DESCENDING VENA CAVA (fig. 170, /, and 

 fig. 171) results from the union of the right and left innominate 

 veins, and brings to the heart the blood of the head and neck, upper 

 limbs, and thorax. 



Its origin is placed behind the junction of the first costal cartilage 

 of the right side with the sternum. From that spot the large vein 

 descends to the pericardium, perforates the fibrous layer of that bag 

 about one inch and a half above the heart, and ends in the right 

 auricle. On its outer surface the vein is covered by the pleura, and 

 the phrenic nerve is in contact with it. To the inner side are the 

 innominate artery and the ascending aorta. Behind the vein is the 

 root of the right lung. 



When the cava is about to perforate the pericardium it is joined 

 posteriorly by the large azygos vein ; and higher up it receives 

 small veins from the pericardium, and the parts in the mediastinum. 



