608 THE ARTERIES. 



CHAPTER III. 

 THE AORTA. 



If we take a general survey of the aorta, we shall find that it arises from the 

 base of the left ventricle, ascends to beneath the dorso-lumbar column, curving 

 backwards and downwards, and reaches the entrance to the pelvis, where it 

 terminates by four branches. It furnishes, besides, about from 2 to 2^ inches 

 from its origin, a secondary trunk, which soon divides into two new arteries, the 

 right and largest of which gives oflf a particular trunk — the common origin of 

 the two long vessels destined for the head. 



This disposition permits us to recognize in the aorta seven principal sections : 



1. The aortic trunk, or common aorta — the source of all the arteries, and 

 giving origin to the anterior and posterior aorta. It only furnishes blood 

 directly to the heart itself. 



2. T\iQ 2^osterior aorta— the real continuation of the common aorta — is distri- 

 buted to the posterior moie:y of the trunk and to the abdominal limbs ; it 

 terminates by a double bifurcation. 



3. The internal and, 4, external iliac arteries — branches of this bifurcation 

 which are almost entirely expended in the posterior limbs. 



5. The anterior aorta — the smallest of the two trunks furnished by the 

 common aorta — is chiefly destined for the anterior moiety of the trunk and the 

 thoracic limbs. 



6. The axillary arteries, or brachial trunTcs ; these arise from the bifurcation 

 of the preceding artery, and are continued by their terminal extremity into the 

 fore limbs. 



7. The carotid arteries, or arteries of the head ; these emanate by a common 

 trunk from the right brachial bifurcation. 



Article I. — Aortic Trunk, or Common Aorta. 



The point of departure for all the arteries carrying red blood, the common 

 aorta, proceeds from the left ventricle by becoming continuous with the festooned 

 fibrous zone which circumscribes the arterial orifice of that cavity. It passes 

 upwards and a little forwards, bifurcating, after a course of 2 or 2i inches, into 

 the anterior and posterior aortce. 



Its volume, inferior to that of its two terminal branches, is not uniform ; at 

 its origin, and opposite the sigmoid valves, it presents (an enlargement — the 

 hulhus aortce — caused by) three dilatations, each corresponding to what is de- 

 scribed as the sinus o/the aorta (sinus aortici, simis Valsalvce). 



Included, on the right side, in the crescent formed by the auricular mass ; 

 in relation, on the left side, with the pulmonary artery — which is joined to it by 

 means of cellulo-adipose tissue traversed by the cardiac nerves — the common 

 aorta forms, with the latter artery, a fasciculus enveloped by the visceral layer 

 of the pericardium, which is reflected as a sheath around these two vessels. 



Two collateral arteries are given off directly from the aorta — the cardiac or 

 coronary arteries. 



