Medial and lateral triangles of the neck

General classification and boundaries

The neck is divided by the sternocleidomastoid muscle (m. sternocleidomastoideus) into two main regions:

1. Medial triangle of the neck. It is bounded by the anterior midline of the neck medially, the edge of the mandible superiorly, and the anterior edge of m. sternocleidomastoideus laterally. The hyoid bone divides this space into two subregions:
2. Suprahyoid region: includes the unpaired submental triangle and the paired submandibular triangle.
3. Infrahyoid region: consists of the carotid and omotracheal triangles.

1. Lateral triangle of the neck. Located between the posterior edge of m. sternocleidomastoideus (anteriorly), the anterior edge of the trapezius muscle (posteriorly), and the clavicle (inferiorly). The inferior belly of the omohyoid muscle (m. omohyoideus) further divides it into two triangles: a larger upper one (omotrapezoid triangle) and a smaller lower one (omoclavicular triangle, with the clavicle forming its base).

Suprahyoid region: submental and submandibular triangles

This area is located above the hyoid bone and contains important fascial spaces and glands.

Submental triangle (trigonum submentale) is unpaired. Its apex points to the mental spine, the lateral sides are formed by the anterior bellies of the digastric muscle (m. digastricus), and its base is formed by the hyoid bone. The floor is formed by the mylohyoid muscle (m. mylohyoideus), the fibers of which converge along the midline into a tendinous raphe. Lymph nodes lie in the fatty tissue beneath the second layer of the cervical fascia, collecting lymph from the tip of the tongue, the middle parts of the lower lip, and the floor of the mouth.

Submandibular triangle (trigonum submandibulare) is bounded by the edge of the mandible superiorly and the two bellies of the digastric muscle anteriorly and posteriorly. The bed of the submandibular salivary gland is formed in this region. It is enclosed by the proper (second) fascia of the neck. Important surgical feature: the fascia does not send septa into the gland parenchyma, making it easy to enucleate.

Large vessels pass through the region of the gland. The facial vein lies superficially, while the facial artery lies deep within the fascial bed, heading toward the pharyngeal wall (where there is a risk of injury during tonsillectomy). Nerves include the lingual nerve (n. lingualis) and hypoglossal nerve (n. hypoglossus). Superficial to this, beneath the platysma, runs the marginal mandibular branch of the facial nerve — damage to it causes the patient's corner of the mouth to be pulled upward.

Topography of deep muscles and Pirogov's triangle

Deep muscles of the floor of the oral cavity are located beneath the floor of the submental triangle. Directly above m. mylohyoideus lies the rounded geniohyoid muscle (m. geniohyoideus). Deeper to it is the fan-shaped genioglossus muscle (m. genioglossus), to which the hyoglossus muscle (m. hyoglossus) attaches posteriorly and laterally. The lingual nerve, lingual vein, and sublingual salivary gland lie in the cleft between the latter two muscles.

In surgery, a specific landmark is used to access the lingual artery — Pirogov's triangle.

• Superiorly it is bounded by the hypoglossal nerve.
• Anteriorly — by the posterior edge of m. mylohyoideus.
• Inferiorly and posteriorly — by the tendon of the posterior belly of the digastric muscle.

The floor of this small triangle is formed by m. hyoglossus. To reach the lingual artery, the surgeon must bluntly separate the fibers of this muscle, as the artery lies deep to it, whereas the vein runs superficially.

Infrahyoid part of the neck

Inferior to the hyoid bone (pars infrahyoidea) lie the carotid and omotracheal triangles. Vital organs are concentrated in this zone: the larynx, trachea, thyroid and parathyroid glands (anteriorly and laterally), as well as the pharynx and esophagus (posteriorly).

Omotracheal triangle (trigonum omotracheale) is bounded by the superior belly of the omohyoid muscle, the anterior edge of m. sternocleidomastoideus, and the anterior midline of the neck. When studying the layered structure, attention is drawn to the platysma (platysma): it covers only the upper outer parts of this triangle, while in the central part (above the jugular notch) its muscle fibers are absent.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Layered structure of the omotrapezoid and omoclavicular triangles of the neck
• Detailed topography and contents of the carotid triangle (trigonum caroticum)
• Fasciae of the neck according to V.N. Shevkunenko and interfascial fascial spaces
• Syntopy of the organs of the omotracheal triangle (larynx, trachea, thyroid gland)
• Formation and branches of the superficial cervical loop (arcus cervicalis superficialis)

Other topics in "Topographic Anatomy of the Neck"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.