The anterior jugular vein, in its course down the neck, communicates freely with the inter nal and external jugular veins, and sometimes terminates by opening into the latter.
It receives branches from the larynx, and sometimes from the thyroid gland.
Not unfrequently the veins of opposite sides are connected by a transverse branch, which crosses the trachea immediately above the sternum, and receives the terminations of some of the inferior thyroid veins, and of one or two subcutaneous veins from the thorax.
Internal jugular blood which has circulated through the brain and sinuses of the dura mater, is returned by the great lateral sinus to the internal jugular vein, which extends from the posterior part of the foramen lacerum posterius, to the root of the neck, where on each side it forms the vena in norninata, by its union with the subclavian vein.
Its direction is strictly vertical.
At its commencement this vein presents an oval dilatation (sinus, or gulph of the internal jugular vein), which is lodged in the jugular fossa, and into which the inferior petrosal sinus of the dura mater opens. The internal ju gular vein is placed posterior, and external, to the internal carotid artery, (the lingual, glosso pharyngeal, and pneumogastric nerves inter vening,) and rests upon the anterior surface of the rectus capitis lateralis muscle ; but as the vein is traced downwards, it will be found, a little below the base of the skull, to lie parallel with, and to the outer side of, the internal carotid ; the spinal accessory nerve here de scends upon the anterior surface of the vein. Subsequently, the internal jugular vein enters the sheath of the common carotid artery, along with the vagus nerve, and preserves the same relative position to that great vessel as it did to its internal branch. At the root of the neck the vein of the right side intersects, at right angles, the front of the first stage of the subclavian artery ; on the left side, the vein, whilst it is anterior, is at the same time parallel, to the thoracic stages of the sub clavian and carotid arteries.
Collateral branches of the internal jugular vein.—Opposite the corn u of the os hyoides, the internal jugular vein is joined by (a) the facial vein, and sometimes by (b) a large communi cating branch front the temporo-maxillary vein, by which its size is sensibly augmented ; above the os hyoides, it receives (c) the pharyngeal vein, derived from a venous plexus on the sides and back of the phanynx ; (d), the proper lin gual veins, two in number, " venm comites " of the lingual artery, the course of which they accurately follow : the lingual veins, as has been already stated, sometimes form a trunk of considerable size, by uniting with the facial vein *; and (e), the occipital vein, which has been described in the preceding page. Below
the level of the os hyoides, the internal jugular vein receives (f) a laryngeal branch, which escapes from the larynx through an opening in the thyro-hyoid membrane ; (g), the supe rior thyroid veins, " venm comites " of the superior thyroid artery, and which emanate from the superficial and upper portions of the thyroid gland : these occasionally terminate in the anterior jugular vein, or in the common trunk of the facial and lingual veins when it is present; and (h) the middle thyroid veins, which pass out from the lower part of the lateral lobe of the gland, and join the most inferior portion of the internal jugular vein.
The vertebral vein. — The vertebral vein arises by muscular branches, which are deeply placed at the base of the skull, in the vicinity of the foramen magnum, and first exists as a distinct trunk in the foramen of the transverse process of the atlas, where it is joined by two communicating branches, one of which passes through the posterior condy loid foramen, and opens into the great lateral sinus, whilst the other is derived from the oc cipital vein.
The course and relations of the vertebral vein, from this to its termination, are iden tical with those of the cervical stage of its corresponding artery, which it accompanies through the foramina in the transverse pro cesses of the cervical vertebrm. On issuing from the foramen of the sixth vertebra, it is joined by the veins which accompany the ar teria cervicalis profunda and the arteria cer vicalis superficialis. Lastly, the vertebral vein usually passes behind the subclavian artery on the right side, and in front of that vessel, on the left side, to terminate in the vena inno minata. Sometimes, though rarely, the ver tebral ends in the internal jugular vein.* The vertebral veins anastomose very freely with the spinal veins, as well with those which are within the spinal canal, as with those which are external to the vertebrm, by means of small branches which enter the foramina, by which the cervical spinal nerves issue.