598 THE BLOOD-VASCULAR SYSTEM. 



It communicates with the anterior jugular, and, in the substance of the parotid, 

 receives a large branch of communication from the internal jugular. 



The Posterior External Jugular Vein commences in the occipital region, and 

 returns the blood from the integument and superficial muscles in the upper and 

 back part of the neck, lying between the Splenius and Trapezius muscles. It runs 

 down the back part of the neck, and opens into the external jugular just below 

 the middle of its course. 



The Anterior Jugular Vein commences near the hyoid bone from the con- 

 vergence of several superficial veins from the submaxillary region. It passes 

 down between the median line and the anterior border of the Sterno-mastoid, 

 and at the lower part of the neck passes beneath that muscle to open into the 

 termination of the external jugular or into the subclavian vein (Fig. 331). This 

 vein varies considerably in size, bearing almost always an inverse proportion to the 

 external jugular. Most frequently there are two anterior jugulars, a right and 

 left, but occasionally only one. This vein receives some laryngeal veins, and 

 occasionally a small thyroid vein. Just above the sternum the two anterior 

 jugular veins communicate by a transverse trunk, which receives tributaries from 

 the inferior thyroid veins. It also communicates with the internal jugular. There 

 are no valves in this vein. 



The Internal Jugular Vein collects the blood from the interior of the cranium, 

 from the superficial parts of the face, and from the neck. It commences just 

 external to the jugular foramen, at the base of the skull, being formed by the 

 coalescence of the lateral and inferior petrosal sinuses (Fig. 329). At its origin it 

 is somewhat dilated, and this dilatation is called the sinus, or gulf, of the internal 

 jugular vein. It runs down the side of the neck in a vertical direction, lying at 

 first on the outer side of the internal carotid, and then on the outer side of the 

 common carotid, and at the root of the neck unites with the subclavian vein to 

 form the innominate vein. The internal jugular vein, at its commencement, lies 

 upon the Rectus capitis lateralis, and behind the internal carotid artery and the 

 nerves passing through the jugular foramen ; lower down, the vein and artery lie 

 upon the same plane, the glosso-pharyngeal and hypoglossal nerves passing forward 

 between them ; the pneumogastric descends between and behind them in the same 

 sheath, and the spinal accessory passes obliquely outward, behind or in front of, 

 the vein. 'At the root of the neck the vein of the right side is placed at a little 

 distance from the artery ; on the left side it usually lies over the artery at its 

 lower part. The right internal jugular vein crosses the first part of the subclavian 

 artery. The vein is of considerable size, but varies in different individuals, the 

 left one being usually the smaller. It is provided with a pair of valves, which 

 are placed at its point of termination or from half to three-quarters of an inch 

 above it. 



Tributaries. This vein receives in its course the facial, lingual, pharyngeal. 

 superior and middle thyroid veins, and sometimes the occipital. At its point of 

 junction with the common facial vein it becomes greatly increased in size. 



The lingual veins commence on the dorsum, sides, and under surface of the 

 tongue, and, passing backward, following the course of the lingual artery and its 

 branches, terminate in the internal jugular. Sometimes the ranine vein, which is 

 a branch of considerable size commencing below the tip of the tongue, joins the 

 lingual. Generally, however, it passes backward, crosses the Hyo-glossus muscle 

 in company with the hypoglossal nerve, and joins the facial. 



The pharyngeal vein commences in a minute plexus, the pharyngeal, at the 

 back part and sides of the pharynx, and, after receiving meningeal tributaries 

 and the Vidian and spheno-palatine veins, terminates in the internal jugular. It 

 occasionally opens into the facial, lingual, or superior thyroid vein. 



The superior thyroid vein commences in the substance and on the surface of 

 the thyroid gland by tributaries corresponding with the branches of the superior 

 thyroid artery, and terminates in the upper part of the internal jugular vein. It 

 receives the superior laryngeal and crico-thyroid veins. 



