The<unk>  is about 5 cm. in length. It commences at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart’s axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm. behind the posterior surface of the sternum.
At its origin it presents, opposite the segments of the<unk> rtic valve, three small dilatations called the<unk> rtic sinuses.
At the union of the<unk>  with the<unk> rtic arch the caliber of the vessel is increased, owing to a bulging of its right wall.
This dilatation is termed the bulb of the<unk> rta, and on transverse section presents a somewhat oval figure.
The<unk>  is contained within the pericardium, and is enclosed in a tube of the serous pericardium, common to it and the pulmonary artery.
Ascending aorta
Descending aorta
Thoracic aorta
Coronary sinus
Aortic sinus
Pericardiacophrenic artery
Inferior vena cava
Superior vena cava