Anterior Triangle of the Neck and its Subdivisions

Original Author: Oliver Jones
Last Updated: October 27, 2017
Revisions: 27

The anterior triangle of the neck is an anatomical division created by the muscles of the head and neck. It is used clinically to locate structures that pass through the neck. In this article, we shall look at the regional anatomy of the anterior triangle and its subdivisions.

It is important to note that all triangles mentioned here are paired – they will appear on the left and the right side of the neck.


Anterior Triangle

The anterior triangle is situated at the front of the neck.

It is bounded:

  • Superiorly – Inferior border of the mandible (jawbone)
  • Laterally – Medial border of the sternocleidomastoid
  • Medially – Imaginary sagittal line down midline of body
Fig 1.0 - Anterior and posterior triangles of the neck. Note the overlying platysma muscle has been removed

Fig 1.0 – Anterior and posterior triangles of the neck. Note the overlying platysma muscle has been removed

It can be subdivided into 4 further triangles, which we will look at later on.

The anterior triangle of the neck contains muscles, nerves, arteries, veins and lymph nodes.

The muscles in this part of the neck are divided as to where they lie in relation to the hyoid bone. There are four suprahyoid muscles (stylohyoid, digastric, mylohyoid, and geniohyoid) and four infrahyoid muscles (omohyoid, sternohyoid, thyrohyoid, and sternothyroid)

With respect to the vasculature, the common carotid artery passes through the anterior triangle, and bifurcates within the triangle into the external and internal carotid arteries. The internal jugular vein also can be found within this area. It drains blood from the head and neck.

Numerous cranial nerves are located in the anterior triangle. Some pass straight through, and others give off branches to innervate some of the other structures within the triangle. The cranial nerves in the anterior triangle are the facial [VII], glossopharyngeal [IX], vagus [X],accessory [XI], and hypoglossal [XII] nerves.


Subdivisions

The hyoid bone, suprahyoid and infrahyoid muscles are used to further subdivide the anterior triangle into four triangles. We shall look at the borders and contents of each.

Carotid Triangle

The carotid triangle of the neck has the following boundaries:

  • Superior: Posterior belly of the digastric muscle.
  • Lateral: Medial border of the sternocleidomastoid muscle.
  • Inferior: Superior belly of the omohyoid muscle.

The main contents of the carotid triangle are the common carotid artery (which bifurcates within the carotid triangle into the external and internal carotid arteries), the internal jugular vein, and the hypoglossal and vagus nerves.

Fig 1.1 - Carotid triangle of the neck

Fig 1.1 – Carotid triangle of the neck

Clinical Relevance: Medical Uses of the Carotid Triangle

In the carotid triangle, many of the vessels and nerves are relatively superficial, and so can be accessed by surgery. The carotid arteries, internal jugular vein, vagus and hypoglossal nerves are frequent targets of this surgical approach.

The carotid triangle also contains the carotid sinus –  a dilated portion of the common carotid and internal carotid arteries. It contains specific sensory cells, called baroreceptors. The baroreceptors detect stretch as a measure of blood pressure.  The glossopharyngeal nerve feeds this information to the brain, and this is used to regulate blood pressure.

In some people, the baroreceptors are hypersensitive to stretch. In these patients, external pressure on the carotid sinus can cause slowing of the heart rate and a decrease in blood pressure. The brain becomes underperfused, and syncope results. In such patients, checking the pulse at the carotid triangle is not advised.

Submental Triangle

The submental triangle in the neck is situated underneath the chin. Its main content is the submental lymph nodes, which filter lymph draining from the floor of the mouth and parts of the tongue.

It is bounded:

  • Inferiorly – Hyoid bone.
  • Medially – Imaginary sagittal midline of the neck.
  • Laterally – Anterior belly of the digastric.

The base of the submental triangle is formed by the mylohyoid muscle, which runs from the mandible to the hyoid bone.

Fig 1.2 - The submental triangle

Fig 1.2 – The submental triangle


Submandibular Triangle

The submandibular triangle is located underneath the body of the mandible. It contains the submandibular gland (salivary), and lymph nodes. The facial artery and vein also pass through this area.

The boundaries of the submandibular triangle are:

  • Superiorly: Body of the mandible.
  • Anteriorly: Anterior belly of the digastric muscle.
  • Posteriorly: Posterior belly of the digastric muscle.
Fig 1.3 - Lateral view of the neck, showing the submandibular triangle

Fig 1.3 – Lateral view of the neck, showing the submandibular triangle


Muscular Triangle

This anatomical area is situated more inferior than the triangular sub-divisions. It is a slightly dubious triangle, in reality having four boundaries. The muscular triangle is also unique in containing no vessels of note. It does however contain some muscles and organs – the infrahyoid muscles, the pharynx, and the thyroid, parathyroid glands.

The boundaries of the muscular triangle are:

  • Superiorly: The hyoid bone.
  • Medially: Imaginary midline of the neck.
  • Supero-laterally: Superior belly of the omohyoid muscle.
  • Infero-laterally: Inferior portion of the sternocleidomastoid muscle.
Fig 1.4 - Anterior view of the neck, showing the muscular triangle.

Fig 1.4 – Anterior view of the neck, showing the muscular triangle.

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Quiz

Question 1 / 13
Which of the following is not a border of the anterior triangle?

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Question 2 / 13
Which subdivision of the anterior triangle is notable in that it contains no significant blood vessels?

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Question 3 / 13
Which of the following cranial nerves can be found in the anterior triangle?

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Question 4 / 13
Which important structure bifurcates within the carotid triangle?

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Question 5 / 13
Which subdivision of the anterior triangle is made up mostly of lymph nodes?

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Question 6 / 13
Which triangle does the facial artery and vein pass through?

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Question 7 / 13
What is the superior attachment of the muscular triangle?

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Question 8 / 13
The base of the submental triangle is formed by which muscle?

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Question 9 / 13
What is the name of the muscle highlighted in green that serves as the lateral border of the anterior triangle?

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Question 10 / 13
What is the sub-division of the anterior triangle highlighted in red?

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Question 11 / 13
What is the sub-division of the anterior triangle highlighted in red?

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Question 12 / 13
What is the sub-division of the anterior triangle highlighted in red?

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Question 13 / 13
What is the sub-division of the anterior triangle highlighted in red?

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