114 THE ANATOMY OF THE HOESE. 



arteries. It is of great calibre, but not more than three inches ii 

 length. It springs from- the left ventricle, and divides into tW' 

 unequal vessels — the anterior and the posterior aorta. Where th 

 vessel springs from the ventricle it shows, when injected, thre^ 

 bulgings, each corresponding to a sinus of Valsalva. From two o 

 these sinuses spring the right and left coronary arteries of the heart 

 These, which are the first collateral branches of the arterial tree, an 

 described with the heart. 



The Posterior Aoeta is by far the longer of the two terminal branchei 

 of the common trunk, and it has also the greater calibre. It passe; 

 backwards and upwards, describing a curve — the aixh of the aorta, am 

 reaches the spine at the 10th dorsal vertebra. From that point it ii 

 continued backwards along the vertebral bodies, being at first a little t( 

 the left of the middle line ; but it gradually inclines to the right, until 

 at the 14th dorsal vertebra, it lies almost entirely to the right of thi 

 median plane of the body. It passes into the abdominal cavity througl 

 the hiatus aorticus — an opening between the pillars of the diaphragm 

 The arch of the vessel is crossed to the right by the oesophagus, and bi 

 the termination of the trachea. The remaining portion of the arter^ 

 is related on its right to the thoracic duct and vena azygos, the due- 

 being usually between the vein and artery, but sometimes to the left o 

 the latter. The thoracic branches of the posterior aorta are : — 



1. Tire Broncho-cesophageal Artery. — This vessel will be more con 

 veniently dissected with the right side of the chest. It is described ai 

 page 119. 



2. Intercostal Arteries. — The last thirteen of these generally have thii 

 origin. They spring from the upper aspect of the artery, and pass ovei 

 the vertebral bodies, crossing beneath the dorsal cord of the sympathetii 

 to gain the upper end of an intercostal space. Here each gives off i 

 large dorso-spinal branch, and places itself at the posterior border of i 

 rib, along which it descends. The latter .part of the intercostals anc 

 their dorso-spinal branches have already been followed in the dissectior 

 of the chest-wall and back. 



The Anterior Aorta. This vessel, after a course of not more thar 

 three inches, divides into two vessels of unequal size. The left anc 

 smaller of the two is the left axillary artery ; the other is the arteria in 

 nominata. The direction of the anterior aorta is oblique upwards anc 

 forwards, and it is in great part included within the pericardial sac. Ii 

 has no collateral branches of a size meriting description. Of its tormina 

 branches only the left axillary will be followed now. The left axillarj 

 is the vessel for the supply of the neck, the fore limb, and the subjaceni 

 part of the chest-wall on the left side ; while the arteries innominata 

 besides supplying the corresponding parts on the opposite side, carries 

 blood for the head. 



