118 DISTRIBUTION OF THE ARTERIES. 



The remaining vessels of the brain are derived from the 

 vertebral artery, which gives off posterior arteries to the dura 

 mater, and ramifications to the medulla oblongata. 



The basilar artery sends off branches to the cerebellum. 



THE POSTERIOR AORTA. 



Considerably longer and larger than the anterior is the main 

 trunk, from which are derived the artery of the abdomen, pel- 

 vis, and posterior extremities, in addition to the posterior 

 intercostals, and some few of the thoracic arteries. It com- 

 mences opposite the fourth dorsal vertebra? : from its ori- 

 gin it courses first upward, and then backward, having the 

 pulmonary artery on its left, the termination of the windpipe 

 on its right, then takes a course along the spine, inclining to 

 the left side. From the inferior part of the curvature of the 

 aorta arise the right and left bronchial arteries : these vessels 

 penetrate the lungs in company with the bronchia, to the 

 branches of which they cling in the course of their ramifica- 

 tions within the substance of the lungs. 



The sesophogeal also spring from the concavity of the arch 

 near to the former, and proceed backward to the sesophagus, 

 where it divides into an inferior and superior artery. The 

 intercostal, the remaining branches, come off in pairs from 

 the sujes of the vessel, to supply all those intercostal 

 spaces posteriorly to the last. These arteries run along the 

 lower borders of the ribs, and end about the inferior parts of 

 the chest and abdomen. They furnish, near their origin, 

 small branches, which enter the vertebral canal. Having 

 detached these small vessels, the posterior aorta continues its 

 passage into the abdomen. In making its exit from the chest, 

 it gives off the phrenic or diaphragmatic arteries. 



Within the abdomen, the aorta continues to be firmly fixed 

 to the spine, by its several cellular attachments, as far as 

 the lumbar vertebra, under the body of which it branches 

 into four large arterial trunks. Prior to this division, 

 the abdominal aorta gives off the coeliac aitery, which is 



