Superficial structures of the neck: Anterior triangle

Definitions & Key takeaways

The anterior neck triangle, or just the anterior triangle, is a region of the neck bounded by the inferior border of the mandible superiorly, the anterior border of the sternocleidomastoid laterally, and the sagittal line down the midline of the neck medially.

The anterior triangle is home to several muscles, nerves, arteries, veins, and lymph nodes. Muscles of this region are in two groups: the suprahyoid and infrahyoid muscles. The suprahyoid muscles include the stylohyoid, the digastric, the mylohyoid, and the geniohyoid muscles. The infrahyoid muscles include the omohyoid, the sternohyoid, the thyrohyoid, and the sternothyroid muscles.

Nerves found in the anterior triangle include several cranial nerves, such as CN VII, CN IX, CNX, CN XI, and CN XII. Blood vessels passing through this region include the common carotid artery, which splits into the internal and the external carotid artery supplying various structures in the head. There is also the internal jugular vein, which drains venous blood from the head and neck.

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Introduction0:00–0:37

The neck is the anatomical region between the base of the cranium superiorly and the clavicles inferiorly and it joins the head to the trunk and limbs, serving as a major conduit for structures passing between them.
The neck is divided in two major triangles: anterior and posterior, based mainly on the borders of the sternocleidomastoid, or SCM, and trapezius muscles, as well as other muscular and bony structures found in the neck.
These regions provide a clear location regarding the structures, injuries or pathologies involving the neck. Now, the anterior triangle, like any respectable triangle, has three sides, called boundaries.

Boundaries0:37–1:26

The anterior boundary is formed by the median line of the neck, the posterior boundary is formed by the anterior border of the sternocleidomastoid muscle, or SCM for short, and the superior boundary is formed by the inferior border of the mandible.
The triangle has a superficial boundary or a roof formed by subcutaneous tissue containing the platysma, a deep boundary or a floor formed by the pharynx, larynx and thyroid gland and an apex located at the jugular notch in the manubrium.
And if that wasn’t enough, the anterior triangle is further subdivided by the omohyoid and digastric muscles into four smaller triangles: submental, submandibular, carotid and muscular.
The submental triangle sits right below the chin and contains several small submental lymph nodes and small veins that unite to form the anterior jugular vein.

Submental triangle1:26–1:59

Inferiorly, the submental triangle is bounded by the hyoid body, and laterally by the right and left anterior bellies of the digastric muscles.
The floor is formed by the two mylohyoid muscles which meet in a median fibrous raphe, the apex is located at the mandibular symphysis, and the base is formed by the hyoid bone.

Submandibular triangle1:59–3:37

Next, the submandibular triangle contains the submandibular gland, submandibular lymph nodes, cranial nerve XII which is the hypoglossal nerve, mylohyoid nerve and parts of the facial artery and facial vein.
In addition, in 20% of individuals the marginal mandibular branch of the facial nerve extends below the inferior border of the mandible into the submandibular triangle.
The submandibular triangle is bounded superiorly by the inferior border of the mandible, anteroinferiorly by the anterior belly of the digastric muscle and posteroinferiorly by the posterior belly of the digastric muscle.
Its floor is formed by the mylohyoid and hyoglossus muscles, and its roof by the investing layer of deep cervical fascia.
The hypoglossal nerve enters the submandibular triangle by passing deep to the posterior belly of the digastric muscle and deep to the mylohyoid muscle within the submandibular triangle.
It provides motor innervation to the intrinsic and extrinsic muscles of the tongue. Finally, there are also some spinal nerves in the mix.
C1 fibers travel with the hypoglossal nerve and give off the thyrohyoid branch for the thyrohyoid muscle. Then there’s the superior root of the ansa cervicalis, which is composed of fibers from C1 and C2.
The superior root of the ansa cervicalis unites with the inferior root of the ansa cervicalis, which derives from spinal nerves C2 and C3.
These superior and inferior roots form a loop which gives off branches to supply the omohyoid, sternothyroid, and sternohyoid muscles.
Next, the carotid triangle is bound inferomedially by the superior belly of the omohyoid muscle, superiorly by the posterior belly of the digastric muscle and inferolaterally by the anterior border of the SCM.

Carotid triangle3:37–4:47

The carotid triangle contains blood vessels such as the common carotid artery with its branches, the external carotid artery and some of its branches, the internal jugular vein and its tributaries, and also nerves like branches of the vagus nerve, the hypoglossal nerve and superior root of ansa cervicalis, the spinal accessory nerve and branches of the cervical plexus and viscera such as the thyroid gland, larynx, pharynx and deep cervical lymph nodes.
The neurovascular structures in the carotid triangle are surrounded by the carotid sheath. In the carotid sheath, the carotid arteries lie medially, the internal jugular vein lies laterally and the vagus nerve lies posteriorly.
Superiorly, the common carotid artery is replaced by the internal carotid artery and on the anterolateral aspect of the sheath you can find the ansa cervicalis.
Lets take a quick break and see if you can identify all of the different triangles in this image! Speaking of carotids, there are two common carotid arteries: the right common carotid artery which begins at the bifurcation of the brachiocephalic trunk, forming it and the right subclavian artery, and the left common carotid artery which begins at the arch of aorta and ascends into the neck.

Quiz4:47–5:03

Carotid arteries5:03–5:31

Each common carotid artery splits into the internal and external carotid arteries at the upper border of the thyroid cartilage.
The internal carotid arteries give off no named branches in the neck, and they enter the cranium through the carotid canals in the petrous parts of the temporal bones.

Internal carotid artery5:31–6:28

Here, they become the main arteries for the brain and structures in the orbits. The proximal part of each internal carotid artery contains the carotid sinus which is a baroreceptor that reacts to changes in arterial blood pressure and is innervated by the glossopharyngeal nerve through the carotid sinus nerve and also by the vagus nerve.
The carotid body is located in a septum on the deep side of the bifurcation of the common carotid artery in close relation with the carotid sinus.
It is also innervated primarily by the carotid sinus nerve, a branch of the glossopharyngeal nerve, and it acts as a chemoreceptor that monitors the level of oxygen in the blood.
This means that when there are low levels of oxygen, that sends a signal to the brain to increase the respiration rate. The external carotid arteries supply most structures external to the cranium and they run posterosuperiorly to the region between the neck of the mandible and the lobule of the auricle, where they split in two terminal branches: the maxillary artery, which has 3 major branches that supply numerous structures, and the superficial temporal artery, which enters the temporal fossa and supplies regions of the scalp.

External carotid artery6:28–9:18

Before its termination, it gives off six arteries: the superior thyroid artery, ascending pharyngeal artery, lingual artery, facial artery, occipital artery and posterior auricular artery.
A good mnemonic to remember the branches of the external carotid artery in order from which branches first is “Some Anatomists Like Freaking Out Poor Medical Students”, where the first four branches arise from the anterior aspect, and the last four, from the posterior aspect.
So first, there’s the superior thyroid artery, which runs deep into the infrahyoid muscles to supply the thyroid gland. It also supplies the infrahyoid muscles and SCM and gives a branch called the superior laryngeal artery which supplies the larynx.
Second, there’s the ascending pharyngeal artery, which ascends to the pharynx giving branches to the pharynx, prevertebral muscles, middle ear and cranial meninges.
Third, the lingual artery runs deep to the hypoglossal nerve, the stylohyoid muscle and the posterior belly of the digastric muscle and gives branches to the posterior tongue.
Then it turns superiorly at the anterior border of the hyoglossus muscle and splits into two branches: the deep lingual artery and the sublingual artery.
Fourth, the facial artery gives rise to the ascending palatine artery and the tonsillar artery. Then it passes obliquely beneath the digastric and stylohyoid muscles and the angle of the mandible, and it gives rise to the submental artery to the floor of the mouth and hooks around the middle of the inferior border of the mandible to enter the face.
It is the major arterial supply of the face, giving rise to several branches on its route towards the medial angle of the eye.
Fifth, the occipital artery arises from the posterior aspect and ends in the posterior part of the scalp where it splits into numerous branches.
The posterior auricular artery arises from the posterior aspect and it ascends posteriorly between the external acoustic meatus and mastoid process to supply the neighboring muscles, parotid gland, facial nerve and structures in the temporal bone, auricle and scalp.
Finally, the two terminal branches, namely the maxillary artery and the superficial temporal artery, arise from the external carotid all the way up in the head.
Now that we just learned about the major vessels in the neck, can you label all of the branches from the external carotid artery?
Now let’s switch gears and look at the internal jugular vein, or IJV, which is the largest vein in the neck. In fact, most veins in the anterior region are tributaries to it.
It starts at the jugular foramen in the posterior cranial fossa as a direct continuation of the sigmoid sinus, and descends laterally in the carotid sheath.

Quiz9:18–9:29

The vein leaves the anterior cervical region by passing deep to the gap between the sternal and clavicular heads of the sternocleidomastoid muscle.

Internal jugular vein9:29–10:33

Posterior to the sternal end of the clavicle, the internal jugular vein merges with the subclavian vein to form the brachiocephalic vein.
The inferior end of the vein dilates to form the inferior bulb of the vein, which has a bicuspid valve that allows blood to flow toward the heart and prevent backflow into the vein.
Tributaries of IJV are the inferior petrosal sinus, facial, lingual, pharyngeal, superior and middle thyroid veins which drains blood from the brain, anterior face, cervical viscera and deep muscles of the neck.
And finally, there’s the muscular triangle or the omotracheal triangle, which is bounded superolaterally by the superior belly of the omohyoid muscle, inferolaterally by the anterior border of SCM and medially by the median plane of the neck.
This triangle contains the sternothyroid and sternohyoid muscles, as well as the thyroid and parathyroid glands. Now, muscles in the anterior triangle are represented by the hyoid muscles.

Muscular triangle10:33–10:59

These muscles steady or move the hyoid and larynx and are divided into suprahyoid and infrahyoid muscles. So, the suprahyoid muscles connect the hyoid to the cranium and includes 4 muscles: mylohyoid, geniohyoid, stylohyoid and digastric.
The mylohyoid muscle arises from the mylohyoid line of the mandible and attaches to the mylohyoid raphe and the body of the hyoid.

Suprahyoid muscles10:59–13:03

It’s innervated by the nerve to mylohyoid, a branch of the trigeminal nerve, and elevates the hyoid, the floor of the mouth and the tongue during speaking and swallowing.
The geniohyoid muscles are immediately superior to the mylohyoid muscles. They arise from the inferior mental spine of the mandible and attach to the hyoid body.
It’s innervated by C1 via the hypoglossal nerve and pulls the hyoid anterosuperiorly, and it also shortens the floor of the mouth and widens the pharynx.
The stylohyoid muscle arises from the styloid process of temporal bone and it attaches to the hyoid body. It’s innervated by the stylohyoid branch of the facial nerve and it elevates and retracts the hyoid, and so it elongates the floor of the mouth, which comes in handy during swallowing.
The digastric muscle translates as “two bellies” - so there’s the anterior belly which arises from digastric fossa of the mandible, and the posterior belly which arises from the mastoid notch of the temporal bone.
The two bellies are united by an intermediate tendon and attach to the body and greater horn of the hyoid bone. The anterior belly is innervated by the nerve to the mylohyoid and the posterior belly is innervated by the digastric branch of the facial nerve.
Its role is to work with the infrahyoid muscles to depress the mandible against resistance and it elevates and steadies the hyoid during swallowing and speaking.
Then, there are the infrahyoid muscles, which anchor the hyoid inferiorly and depress it. These four muscles are arranged in two planes: a superficial plane, made up of the sternohyoid and omohyoid, and a deep plane, composed of the sternothyroid and thyrohyoid muscles.
And a pro tip is that the names of these muscles indicate where they originate and insert! So the sternohyoid muscle arises from the manubrium of the sternum and the medial end of the clavicle and inserts on the hyoid body.

Infrahyoid muscles13:03–14:49

It’s innervated by C1-C3 by a branch of the ansa cervicalis and it depresses the hyoid after elevation during swallowing.
Next, there’s the omohyoid muscle, which has two bellies, a superior and an inferior one, which are united by an intermediate tendon.
With this muscle, “omo” refers to the scapula, so it arises from the superior border of the scapula near the suprascapular notch, and it attaches to the inferior border of hyoid.
It’s innervated by C1-C3 by a branch of ansa cervicalis and depresses, retracts and steadies the hyoid. Then, there’s the sternothyroid muscle, which arises from the posterior surface of the manubrium, and it attaches to the oblique line of thyroid cartilage.
It’s innervated by C2 and C3 by a branch of ansa cervicalis and depresses the hyoid and larynx. The thyrohyoid muscle arises from the oblique line of thyroid cartilage, and it attaches to the inferior border of the body and greater horn of the hyoid.
It’s innervated by C1 via hypoglossal nerve and depresses the hyoid and elevates the larynx.Finally, let’s try to label the hyoid muscles on this image.
All right, as a quick recap. The anterior triangle has the following boundaries: an anterior boundary formed by the median line of the neck, a posterior boundary formed by the anterior border of the SCM, and a superior boundary formed by the inferior border of the mandible.
Furthermore, the anterior triangle is subdivided by the omohyoid and digastric muscles into four smaller triangles: submental, submandibular, carotid and muscular.
The submental triangle contains several small submental lymph nodes and small veins that unite to form the anterior jugular vein.

Quiz14:49–14:59

The submandibular triangle contains the submandibular gland, submandibular lymph nodes, hypoglossal nerve, mylohyoid nerve and parts of the facial artery and facial vein.

Review14:59–17:06

The carotid triangle contains the common carotid artery with its branches, the internal jugular vein and its tributaries, the vagus nerve, the external carotid artery and some of its branches, the hypoglossal nerve and superior root of ansa cervicalis, the spinal accessory nerve, the thyroid gland, larynx, pharynx, deep cervical lymph nodes and branches of the cervical plexus.
The muscular triangle contains the infrahyoid muscles and the thyroid and parathyroid glands. The common carotid artery splits into the internal carotid artery which doesn’t give any branches for the neck and the external carotid artery which has numerous branches such as superior thyroid artery, ascending pharyngeal artery, lingual artery, facial artery, occipital artery and posterior auricular artery and two terminal branches: maxillary artery and superficial temporal artery..
Muscles of the anterior triangle are represented by the suprahyoid and infrahyoid muscles. The suprahyoid muscles are represented by mylohyoid, geniohyoid, stylohyoid and digastric muscles and the infrahyoid muscles are represented by sternohyoid, omohyoid, sternothyroid and thyrohyoid muscles.
and parathyroid glands. The common carotid artery splits into the internal carotid artery, which doesn't give any branches for the neck and the external carotid artery, which has numerous branches such a superior, thyroid, artery ascending pharyngeal, artery lingual, artery facial, artery occipital, artery and posterior, auricular artery, and two terminal, branches, maxillary artery and superficial temporal artery.
Muscles of the anterior triangle are represented by the super highlight and infrahyoid muscles. The superhighway muscles are represented by mylohyoid geniohyoid stylohyoid and that gastric muscles and the infrahyoid muscles are represented by sternohyoid omohyoid sternothyroid and thyrohyoid muscles.