328 DISSECTION OF THE THORAX. 



the right side of the air tube. On its right is the innominate vein of the 

 same side (h). Usually no lateral branch arises from the artery. 



LEFT COMMON CAROTID ARTERY (e). 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 close 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 (17), and the remains of the thymus 

 gland. At first it lies on the trachea, but it crosses afterwards 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. 



In the neck the connections of the vessels of opposite sides are not the 

 same (p. 120). 



The LEFT SUBCI.AVIAN ARTERY (d) ascends to the neck through the 

 upper aperture of the thorax. Beyond the first rib the vessels of opposite 

 sides are alike (p. 118). 



The trunk is directed almost vertically from the arch of the aorta to the 

 inner margin of the first rib. In the thorax the vessel lies deeply, resting 

 at first on the oesophagus, and afterwards on the vertebral column and 

 the longus colli muscle. It is invested by the left pleural bag in all 

 its extent. On its inner side is the trachea, and near the upper opening 

 of the thorax the oesophagus with the thoracic duct is inside it. Some- 

 what anterior to the level of the artery, though running in the same direc- 

 tion, are some of the cardiac nerves. 



VEINS OF THE HEART (fig. 105). In addition to the cardiac veins (p. 

 314) there are the superior and inferior cava, and the pulmonary veins : 

 the former are the great systemic vessels which return impure blood to 

 the right auricle ; and the latter convey pure blood from the lungs into the 

 left auricle. 



The SUPERIOR or DESCENDING CAVA (/) 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 on the right side of the sternum, opposite the interval 

 between the cartilages of the first two ribs. 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 is the ascending part of the arch 

 of the aorta. Behind the vein is the root of the right lung. 



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

 large azygos vein of the thorax (k) ; and higher up it receives small veins 

 from the pericardium, and the parts in the mediastinal space. 



The innominate veins are united inferiorly in the trunk of the descend- 

 ing cava. They are two in number, right and left; and each is formed 

 near the inner end of the clavicle, by the union of the subclavian and in- 

 ternal jugular veins. The trunks differ in length and direction, and in 

 their connections with the surrounding parts. 



The right vein (A) is about one inch and a half long, and descends ver- 

 tically, on the right side of the innominate artery, to its junction with the 

 vein of the opposite side. On the outer surface the pleura covers it, and 

 along it the phrenic nerve is placed. 



