242 THE AORTA. 



The Aorta, as well as the Pulmonary Artery, for a small 

 distance from the heart, is invested by the pericardium ; and, 

 when that sac is opened, appears to be contained in it. 



After crossing the right branch of the Pulmonary Artery, 

 a ligament is inserted into it, which proceeds from the main 

 trunk of the pulmonary artery at its division : this ligament was 

 the Canalis Arteriosus in the foetus. 



As the Aorta proceeds dowfi the spine, it is situated between 

 the two lamina of the mediastinum, and in contact with the 

 left lamen, through which it may be seen. It descends between 

 the crura of the diaphragm, in a vacuity which is sufficiently 

 large to admit of its passage without pressure from the sur- 

 rounding parts, and is still in contact with the anterior surface 

 of the spine, but rather to the left of the middle of it. It con- 

 tinues this course along the spine until it arrives at the cartilag- 

 inous substance between the fourth and fifth lumbar vertebrae, 

 when it divides into two great branches of equal size, which 

 form an acute angle with each other. These are denominated 

 the Common or Primitive Iliac arteries. 



From the Aorta in this course are sent off the arteries which 

 are distributed to all the parts of the body for their nourishment 

 and animation. 



From the curve proceed the great branches which supply 

 the heart, the head, the upper extremities, and part of the tho- 

 rax. Between the curve and the great primitive iliac arteries, 

 the Aorta sends off those branches which supply the viscera 

 contained in the cavities of the thorax and abdomen,* and part 

 of the trunk of the body. The great Iliac branches of the 

 Aorta are divided into smaller arteries, which supply the 

 whole of the lower extremities and some of the viscera of the 

 pelvis. 



Of the Branches which go off from the Arch of the Aorta. 



The proper arteries of the heart, denominated Coronary 

 Arteries, proceed from the Aorta so near to the heart that 



* It ought to be observed here, that the viscera, in the lower part of the 

 pelvis, receive some branches from the internal iliac arteries. 



