The Anatomy of Jugular Veins

The veins that drain the brain

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The jugular veins are found in the neck. There is a pair of internal jugular veins (right and left) and a pair of external jugular veins. They are the main path for deoxygenated blood returning from the cranium back to the heart. The external jugular veins empty into the subclavian veins; the internal jugular veins join with the subclavian veins to form the brachiocephalic veins, which join to form the superior vena cava.

The jugular veins are clinically significant in diagnosing some cardiovascular obstructions as well as useful routes for various types of medication and fluid administration.

Anatomy

The jugular veins are paired right and left. There are four main jugular veins, two internal and two external. There is also a pair of anterior jugular veins.

Location

The largest pair of jugular veins are the internal jugular veins. They exit the cranium through the jugular foramen (foramen is a fancy medical term for a hole). Each of the internal jugular veins runs on either side of the neck under the sternocleidomastoid muscle. They are difficult to locate without ultrasound to assist.

The internal jugular veins join with the subclavian veins to form the brachiocephalic veins. The right internal jugular vein is about 63 millimeters (mm) long while the left internal jugular vein averages about 53 mm long.

The external jugular veins are much smaller in diameter and found much more superficial as compared to the internal jugular veins. They are located outside the sternocleidomastoid muscle and are often visible to the naked eye. The external jugular veins originate at the level of the angle of the mandible and continue to the base of the neck where they empty into the subclavian veins proximal (upstream) to the internal jugular veins.

The anterior jugular veins are located near the midline on either side of the throat. They are very small and not as clinically significant as the internal and external jugular veins.

Structure

The jugular veins are built like all other veins. The walls of veins contain three layers similar to arteries but are much less elastic.

  1. Tunica intima (tunica interna) is the innermost layer that provides a smooth surface for blood to flow.
  2. Tunica media is the muscular middle layer. In veins, it is much thinner than in arteries.
  3. Tunica adventitia (tunica externa) is the outermost layer of the jugular vein and connects it to surrounding tissues.

At the distal (downstream) ends, external and internal jugular veins have one-way valves that prevent blood from flowing backward.

Anatomical Variations

The jugular veins can have significant variation but rarely do those variants have clinical significance. On some people, a second, smaller external jugular vein develops.

Function

Arteries carry blood away from the heart and veins carry blood toward the heart. All veins except those returning blood from the pulmonary system carry deoxygenated blood.

Veins handle much lower pressure than arteries and have much higher capacity overall. At any given time, about 60% to 70% of the body's blood is in the venous system.

The jugular veins are responsible for returning deoxygenated blood from the cranium, face, and brain.

Clinical Significance

The internal and external jugular veins both have clinical significance.

The internal jugular veins are used as a site for central vein catheterization. Typically, locating the internal jugular vein for central line access requires the use of ultrasound. Access to the right internal jugular vein is considered preferable due to its length and straighter route.

The external jugular veins can be used for peripheral intravenous (IV) access in emergency situations when other peripheral IV sites are unavailable. The size of the external jugular veins and relative proximity to the superior vena cava compared to other common IV access points makes them useful for administering large volumes of fluid or blood in patients with traumatic injuries. Unfortunately, placing an IV catheter in the external jugular vein can be very difficult in patients with short or stout necks.

Due to the superficial placement of the external jugular veins, they are useful indicators of systemic venous obstruction. When blood flow is obstructed by something like congestive heart failure, tension pneumothorax, or cardiac tamponade, distended external jugular veins could be a symptom.

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