The left vagus nerve gives off similar branches to the right vagus within the neck and thorax. However, having passed from the skull through the carotid sheaths to the root of the neck, the paths of the two vagi then differ, largely as a result of the disposition of great vessels within the thorax.
The left vagus descends into the thorax between the left common carotid artery and the left subclavian artery. Then it passes posterior to the left brachiocephalic vein and anterior to the arch of the aorta. Passing over the arch of the aorta it gives off its recurrent laryngeal branch which hooks under the ligamentum arteriosum before descending posterior to the arch. Then it gives off many fine branches to the root of the left lung which lies anteroinferiorly. Finally, it passes inferiorly and medially along the anterior surface of the descending aorta before ramifying to form part of the oeophageal plexus. Via the plexus, it contributes the majority of fibres to the anterior vagal trunk.
Hence, the left vagus does not come into as close proximity as the right vagus to the trachea due to the left lateral projection of the arch of the aorta.
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