ARTERIES. 



inches long and is enclosed in both pericardial layers. The 

 right branch, the longer and larger, runs behind the ascending 

 aorta, superior vena cava, and upper right pulmonary vein to 

 the hilus of the right lung. At first it lies below the aortic 

 arch and right bronchus, but above the lower right pulmonary 

 vein; it then crosses in front of the right bronchus. Before 

 entering the hilus it sends a branch along the eparterial 

 bronchus to the upper lobe. The left branch is slightly higher 

 and runs to the hilus of the left lung, passing behind the upper 

 left pulmonary vein, in front of the left bronchus, above the 

 lower left pulmonary vein, and below the aortic arch; the 

 ligamentum arteriosum joins it to the aortic arch. Before en- 

 tering the hilus it sends a branch to the upper lobe. [795] 



Thoracic Aorta. Commencing at the base of the left ven- 

 tricle, this arches upward and backward to the spine; then 

 descending on the spine and passing through the diaphragm, 

 it becomes the abdominal aorta. It is divided into the ascend- 

 ing portion, arch, and descending portion. [797] 



Ascending Aorta. This begins at the left ventricle behind 

 the left margin of the sternum, and opposite the lower border 

 of the third left costal cartilage and the body of the fifth dorsal 

 vertebra. Running upward, forward, and to the right, it be- 

 comes the arch behind the right margin of the sternum, oppo- 

 site the second costal cartilage. At its origin it presents three 

 small dilatations (sinuses of Valsalva) just above the cusps of 

 the aortic valve ; and also a diffuse bulging (great sinus) of the 

 right wall. Its branches are the right and left coronary 

 arteries. [797] 



Arch. This is arched, with the convexity upward, and also 

 curves with the convexity forward and to the left. It runs at 

 first upward, backward, and to the left, in front of the trachea, 

 then passes backward round the left side of the trachea to the 

 left side of the body of the fourth dorsal vertebra, and then 

 descends on this to the lower border of the body, where it 

 becomes the descending aorta. A fibrous relic (ligamentum 

 9 [ 129 ] 



