296 SPECIAL ANATOMY. 



In the embryo, a canal, ductus arteriosus Botalii passes upwards obliquely 

 to the left from the place where the pulmonary artery divides into its two 

 branches, to the concavity of arcus aorta, opposite to the art. subclavia sinis- 

 tra, which at a later period changes into the ligam. arteriosum (one to two 

 lines thick, four long). 



536. II. Pulmonary veins, four, Vena pulmonales s. arteriosa, 



arise from the capillary vessels of Art. pulmonalis and Artt. bronchiales, pass 

 out at the roots of the lungs before the arterial and bronchial branches, two, 

 as well as from the right (at the commencement three), as from the left lung, 

 and sink inside the pericardium behind V. cava super, on the right side and 

 Art. pulmonalis on the left, into the superior part of the left auricle. They 

 possess no valves. The capacity of all four together, is inferior to that of the 

 pulmonary arteries. 



Vessels of the large circulation, Arteries. 



537. Arteria Aorta, the great artery of the body, 



arises above and before from the left ventricle (between septum 

 ventricul. and valv. mitralis), where its root (bulbus aorta) cor- 

 responds to the three semilunar valves, presents internally three 

 pouch-shaped expansions (sinus Valsalva), and externally three 

 elevations (tubera). At the origin circular (in the male thirty- 

 one, in the female twenty-eight Paris lines wide), farther on ellip- 

 tical, anteriorly convex. 



538. Course. It ascends from left to right (aorta ascendens), 

 at the same time a little curved, between Art. pulmon. and V. cava 

 superior. It now bends suddenly backwards, and passes almost 

 horizontally (above the ramus dext. art. pulmonal.} from right to 

 left, and from before backwards, to the left side of the third dorsal 

 vertebra (arcus aorta); whence it descends, after another curva- 

 ture, vertically on the left side of the vertebral column, through 

 the thorax (aorta descendens thoracica), and in the abdomen be- 

 fore the centre of the bodies of the vertebrae, as far as the fourth 

 lumbar vertebra (as aorta desc. abdominalis). Here it divides 

 into its two terminating branches, arteria iliaca. 



539. Aorta ascendens, the ascending Aorta, 



two to two and a half inches long. Position : surrounded by 

 the pericardium ; below, behind Art. pulmonalis, which winds 

 like a screw from before to the left ; behind : ramus dexter art. 

 pulmonalis ; to the right above : V. cava superior ; to the right 

 below : the right auricle. 



