This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Lying oh the deep fascia and beneath the superficial fascia and piatysma is the external jugular vein. This begins below the ear and posterior to the ramus of the jaw, being formed by the union of the temporo-maxillary and posterior auricular veins. It passes downward and slightly backward on the surface of the sternomastoid muscle to its posterior border, which it reaches at about the middle and follows down until about a centimetre above the clavicle; here it pierces the deep fascia and dips behind the clavicular origin of the sternomastoid muscle to empty into the subclavian. It has one pair of valves about 4 cm. above the clavicle, and another pair at its point of entrance into the subclavian. They do not entirely prevent a regurgitation of the blood.
The external jugular vein receives the posterior external jugular vein, and the suprascapular and transverse cervical veins. The occipital may also enter into it. The veins of the neck are exceedingly irregular in their formation and may vary considerably. The external jugular is readily seen through the skin, it may be made more prominent by compressing it iust above clavicle. In operations in this region of the neck in some cases it is necessary to divide this vein; in others one may be able to avoid it, at all events it should be recognized before the incision is made. Behind the angle of the jaw there is usually a branch communicating with the facial, lingual, or internal jugular vein, and just above its lower extremity it is enlarged, forming the part called the sinus. For these reasons, if the vein is cut low down near the clavicle or high up near the angle of the jaw bleeding is liable to be free. The valves are not competent to prevent the reflux of blood and it therefore drains the large internal jugular above and the subclayian below. The attachment of the vein to the deep fascia, as it pierces it above the clavicle, tends to keep its lumen open when the vein is divided and favors the entrance of air into the circulation. The size of the veins in the posterior triangle varies according to those in the anterior. If the anterior and external jugulars are large the posterior and internal jugulars are apt to be small.
- The arteries in the posterior cervical triangle are the subclavian, the transverse cervical, and sometimes the suprascapular when it runs above the clavicle instead of behind it. The line of the subclavian is from the sternoclavicular joint to the middle of the clavicle. It rises about 1.25 cm. (1/2 in.) above the clavicle. The clavicular origin of the sternomastoid muscle covers the inner third of the clavicle so that the subclavian artery is only visible in the posterior cervical triangle from the outer edge of this muscle to the middle of the clavicle. Both the suprascapular and transverse cervical arteries are given off from the thyroid axis, which arises from the first portion of the subclavian just internal to the scalenus anticus muscle. Therefore at their origin they are both considerably above the level of the clavicle, but as they proceed outward they incline downward, and on leaving the outer edge of the sternomastoid muscle the suprascapular is usually behind the clavicle while the transverse cervical runs parallel to it and a short distance (1 cm.) above it, where it can be felt pulsating.
The posterior belly of the omohyoid muscle can be represented by a line drawn from the anterior edge of the sternomastoid muscle opposite the cricoid cartilage, obliquely down and out to the junction of the middle and outer thirds of the clavicle. It is superficial to the transverse cervical artery and at its inner end is above it. These arteries and their accompanying veins will be encountered in operating in these regions for the removal of lymphatic nodes.