114 TOPOGRAPHIC AND APPLIED ANATOMY. 



FIG. 54. The pharynx, esophagus, trachea, and aorta seen from behind. 



important from an operative standpoint ; these are the bronchial, the esophageal, the pericardiac, 

 the mediastinal, and the diaphragmatic. 



Large aneurysms of the descending aorta occasionally erode the vertebras and adjacent 

 ribs and appear in the back alongside of the vertebral column, where they may simulate abscesses. 

 In such cases disagreeable symptoms are produced by pressure upon the intercostal nerves and 

 upon the spinal cord. 



The Pulmonary Artery. The pulmonary artery is united with the ascending aorta by 

 connective tissue (see page 108) and is situated almost entirely within the pericardium. The 

 ascending aorta is upon the right side of the vessel. The pulmonary artery extends from the 

 sternal insertion of the third left costal cartilage to that of the second, and is consequently most 

 easily reached through the second left intercostal space. The vessel, at its origin, is only two 

 centimeters distant from the anterior thoracic wall; it runs backward, upward, and somewhat 

 toward the left and, after a course of about five centimeters, divides outside of the pericardium 

 into a right and a left branch. From the bifurcation, or from the commencement of the left 

 branch, the ligamenlum arteriosum passes to the concavity of the aortic arch. This structure 

 is the remains of the fetal ductus Botalli, which may remain patulous in rare cases. The right 

 branch of the pulmonary artery runs transversely behind the ascending aorta and the superior 

 vena cava to the hilus of the right lung; the left branch is shorter and passes in front of the de- 

 scending aorta to the left lung. 



The pulmonary -veins (double on both sides) are designated as superior and inferior, the 

 superior vein lying also more anteriorly and the inferior vein more posteriorly. The right superior 

 pulmonary vein is situated behind the termination of the superior vena cava in the right auricle; 

 behind this vein are the right pulmonary artery and the right bronchus. The right inferior 

 pulmonary vein lies between the right bronchus and the termination of the inferior vena cava 

 in the right auricle. The superior left pulmonary vein is found in front of the left bronchus 

 and the inferior left pulmonary vein is below the left bronchus. 



The Trachea. The portion of the trachea situated within the mediastinum i. e., the thor- 

 acic portion, in contradistinction to the cervical portion (see page 51) corresponds to that part 

 of the trachea which extends from the lower border of the last cervical vertebra to the fourth 

 dorsal vertebra. In the latter situation the trachea divides into the right and left bronchus. The 

 point of bifurcation, when projected upon the posterior thoracic wall, is situated in the line 

 connecting the inner extremities of the scapular spines (interscapular line); this point corre- 

 sponds to the level of the spinous processes of the third dorsal vertebra, in which situation we 

 auscult respiratory murmurs originating within the trachea. Corresponding with the greater 

 volume of the right lung, the right bronchus is larger than the left and runs more in the direction 

 of the trachea; it is consequently more vertical than the left bronchus. For these reasons foreign 

 bodies in the trachea pass more readily into the right than into the left bronchus. The aortic 

 arch runs backward over the left bronchus (Plate 7); the vena azygos major passes from behind 

 forward over the right bronchus to empty into the superior vena cava (Plates 7 and 8, b). The 

 lower end of the trachea is behind the aortic arch; above the arch, the trachea is found in the 



