This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Internal Jugular Vein should be carefully studied in relation to the common carotid artery of each side. These vessels are contained within a sheath formed by the cervical aponeurosis, and, as has been already stated, the vein lies upon the outer side of each of the common carotid arteries in their two cervical stages: there is, however, at the lower portion of the artery of the left side, a closer connection between it and the internal jugular vein than at the right. Frequently a well-marked aponeurotic septum will be found running from the anterior to the posterior portion of the sheath, so as to divide it into two canals, the inner containing the artery, the outer containing the vein and vagus nerve.