578 THE VASCULAR SYSTEMS 



the ascending aorta, and higher up lies in front of the left auricle on a plane posterior to the 

 ascending aorta. On either side of its origin is the appendix of the corresponding auricle and 

 a coronary artery, the left coronary artery passing, in the first part of its course, behind the 

 vessel. The superficial cardiac plexus lies above its bifurcation, between it and the arch of 

 the aorta. 



The right branch of the pulmonary artery (ramus dexter a. pulmonalis), 

 longer and larger than the left, runs horizontally outward to the root of the right 

 lung, where it divides into two branches, of which the lower and larger supplies 

 the middle and lower lobes; the upper and smaller is distributed to the upper lobe. 

 It has in front of it the ascending aorta, the superior vena cava, and the right phrenic 

 nerve. It has behind it the right bronchus. Above it is the arch of the aorta. 

 Below it is the right auricle. 



The left branch of the pulmonary artery (ramus sinister a. pulmonalis}, 

 shorter and somewhat smaller than the right, passes horizontally to the root of the 

 left lung, where it divides into two branches for the two lobes. In front of it and 

 below it are the pulmonary veins of the left side. Behind are the descending aorta 

 and the left bronchus. Above it are the arch of the aorta, the left recurrent laryn- 

 geal nerve, and the ductus arteriosus. The left bronchus in a portion of its course 

 lies below as well as behind. 



The root of the left pulmonary artery is connected to the under surface of the 

 arch of the aorta by a short fibrous cord, the ligamentum arteriosum; this is the 

 remains of a vessel peculiar to fetal life, the ductus arteriosus. 



The terminal branches of the pulmonary artery will be described with the 

 anatomy of the lung. 



Applied Anatomy. Stenosis of the pulmonary artery, either with, or, more rarely, without 

 defective formation of the interventricular septum, is one of the commonest congenital defects 

 of the heart. It may be due either to fetal endocarditis or to maldevelopment of the bulbus 

 cordis. As in most forms of congenital heart disease, the child is cyanosed (morbus coeruleus), 

 especially when excited or on exertion, and rarely lives to grow up, commonly dying of heart 

 failure in infancy, or of pulmonary tuberculosis or intercurrent disease in childhood. The 

 chief signs of the condition are the loud, harsh systolic cardiac murmur best heard over the 

 second left costal cartilage, cyanosis, clubbing of the finger tips, and the presence of an excess 

 of red corpuscles in the blood. 



Embolism of the pulmonary artery by a clot of blood coming from the right side of the heart 

 in patients with heart disease, or from a thrombosed vein in cases, for example, of influenza, 

 enteric fever, puerperal sepsis, or fractured limbs, is a common cause of sudden or rapid death. 

 The patient may cry out with sudden excruciating pain in the precordia when the detached 

 embolus lodges, and after a brief period of intense dyspnea, pallor, and anguish, die. 



A few cases of surgical interference in embolism of the pulmonary artery are on record. Sev- 

 eral were in a measure successful, death being usually due to septic complications, such as 

 pleurisy and pericarditis. (Cf. Kreuzer, Centralblatt fur Chirurgie, No. 21, 1909. 



THE AORTA (Figs. 431, 432). 



The aorta, or arteria magna, is the main trunk of a series of vessels which convey 

 the oxygenated blood to the tissues of the body for their nutrition. It commences 

 at the upper part of the left ventricle, where it is about one and one-eighth inches 

 (28 mm.) in diameter, and, after ascending for a short distance, arches backward 

 and to the left side, over the root of the left lung, then descends within the thorax 

 on the left side of the vertebral column, passes through the aortic opening in the 

 Diaphragm, and, entering the abdominal cavity, terminates, considerably dimin- 

 ished in size, about seven-tenths of an inch (17.5 mm.) in diameter, opposite the 

 lower border of the fourth lumbar vertebra, where it divides into the right and left 

 common iliac arteries. Hence, it is divided into the ascending aorta, the arch of 

 the aorta, and the descending aorta, which last is again divided into the thoracic 

 aorta and the abdominal aorta, from the position of these parts. 



