Neck boundaries and division into regions
The anatomical boundaries of the neck clearly separate it from the head and the thorax:
- Superior boundary: runs along the base of the mandible to its angle, then extends to the apex of the mastoid process, follows the superior nuchal line, and ends at the external occipital protuberance.
- Inferior boundary: begins at the jugular notch of the sternum, follows the superior border of the clavicle to the acromion of the scapula, and is completed by an imaginary line drawn to the spinous process of the 7th cervical vertebra.
An imaginary frontal plane passing anterior to the trapezius muscles and attaching to the transverse processes of the cervical vertebrae divides the neck into two extensive zones:
- Posterior region (regio cervicalis posterior / regio nuchae): includes the cervical spine, a developed muscular mass, and the vessels and nerves passing through it.
- Anterior region (regio cervicalis anterior): contains the main organs of the neck and the major neurovascular bundles.
External landmarks (top to bottom)
During inspection and palpation of the anterior region of the neck along the midline, the following structures are sequentially identified:
- Hyoid bone: palpable below the mandible (its greater horns are best identified).
- Thyroid cartilage: its laminae form the laryngeal prominence (prominentia laryngea). It is important to remember that the vocal cords (ligg. vocalia) project inferior to the superior thyroid notch.
- Thyrohyoid ligament (lig. thyrohyoideum): stretched between the hyoid bone and the thyroid cartilage, its level corresponds to the lower part of the pharynx.
- Cricoid cartilage: its arch (arcus cartilaginis cricoideae) is palpable as a transverse ridge immediately inferior to the thyroid cartilage.
The level of the 6th cervical vertebra is of particular clinical significance. Two important anatomical transitions occur here: the larynx transitions into the trachea, and the pharynx into the esophagus. Lateral to the cricoid cartilage at this level, the carotid tubercle (tuberculum caroticum) is palpable—the transverse process of the 6th cervical vertebra against which the common carotid artery can be compressed to stop bleeding.
Organ projections and the significance of muscular landmarks
The main muscular landmark of the anterior region is the sternocleidomastoid muscle (m. sternocleidomastoideus). It divides each half of the neck into medial and lateral triangles.
This muscle plays a crucial role in surgical approaches to the carotid arteries:
- In the upper neck, the internal and external carotid arteries are located medial (internal) to the muscle.
- In the lower neck, the muscle completely covers the common carotid artery.
Projections of internal organs:
- Trachea: located along the midline; its first rings are readily accessible for palpation.
- Thyroid gland: the isthmus of the gland lies on the first tracheal rings and shifts during swallowing.
- Esophagus: its projection is shifted slightly to the left of the midline.
Lateral triangle of the neck is bounded inferiorly by the clavicle. In the angle between the clavicle and the m. sternocleidomastoideus, the brachial plexus (plexus brachialis) is projected, and at the midpoint of the superior border of the clavicle lies the trunk of the subclavian artery.
Topography of nerves and superficial veins
The sternocleidomastoid muscle also serves as a guide for locating neural structures. At the midpoint of its posterior border is the emergence point of the cutaneous branches of the cervical plexus:
- Great auricular nerve (n. auricularis magnus): runs toward the angle of the mandible along the course of the external jugular vein.
- Transverse cervical nerve (n. transversus colli): crosses the muscle in a posterior-to-anterior direction.
- Lesser occipital nerve (n. occipitalis minor): ascends along the posterior border of the muscle.
- Supraclavicular nerves (nn. supraclaviculares): descend in the lateral triangle toward the sternum, clavicle, and acromion.
Additionally, the accessory nerve (n. accessorius) is projected along a line from the junction of the upper and middle thirds of the posterior border of the m. sternocleidomastoideus to the outer third of the anterior border of the trapezius muscle. The external jugular vein (v. jugularis externa), running from the angle of the mandible to the midpoint of the clavicle, is contoured superficially to the muscle.
Jugular notch and triangles of the neck
Skeletotopically, the jugular notch of the sternum (incisura jugularis sterni) corresponds to the level of the intervertebral disc between the 2nd and 3rd thoracic vertebrae.
Large vessels may project into this zone:
- The upper margin of the aortic arch (in individuals with a dolichomorphic body type).
- An aberrant right subclavian or left common carotid artery.
- The lowest thyroid artery (a. thyroidea ima), which occurs in 6–8% of cases.
To detail the topography, the anterior region of the neck is divided into a series of triangles. Using the digastric (m. digastricus) and omohyoid (m. omohyoideus) muscles, the following are distinguished: the submental, submandibular, carotid, omotracheal, omotrapezoid, and omoclavicular triangles, as well as the sternocleidomastoid region.
Briefly: answers to topical questions
Which muscles bound the carotid triangle of the neck?
The carotid triangle of the neck (trigonum caroticum) is bounded by three muscles.
- Posterior belly of the digastric muscle (m. digastricus) — bounds the triangle superiorly.
- Sternocleidomastoid muscle (m. sternocleidomastoideus) — forms the lateral boundary.
- Superior belly of the omohyoid muscle (m. omohyoideus) — bounds the triangle inferiorly.
What anatomical structures form the boundaries of the lateral triangle of the neck?
The lateral triangle of the neck (trigonum colli laterale) is a paired region bounded by the following anatomical structures.
- Clavicle — forms the inferior boundary of the triangle.
- Sternocleidomastoid muscle (m. sternocleidomastoideus) — bounds the region anteriorly, as the lateral triangle is located lateral to it.
Sources do not specify the exact posterior boundary, but it is noted that the accessory nerve passes through this region, heading toward the anterior border of the trapezius muscle.
What cervical fasciae are distinguished according to V.N. Shevkunenko's classification?
According to V.N. Shevkunenko's classification, five fasciae are distinguished in the neck.
- Superficial fascia (fascia superficialis, s. subcutanea) — forms a sheath for the m. platysma.
- Superficial layer of the deep cervical fascia (lamina superficialis fasciae colli propriae) — forms sheaths for the m. sternocleidomastoideus and m. trapezius.
- Deep layer of the deep cervical fascia (lamina profunda fasciae colli propriae) — forms sheaths for the infrahyoid muscles.
- Endocervical fascia (fascia endocervicalis) — is divided into parietal and visceral layers, forming the sheath of the neurovascular bundle.
- Prevertebral fascia (fascia prevertebralis) forms sheaths for the deep muscles of the neck.
Into which triangles is the anterior region of the neck divided?
Each half of the anterior neck region is divided by the sternocleidomastoid muscle into two main triangles: medial and lateral. Smaller triangles are distinguished within them.
- The medial triangle includes: the submental triangle (trigonum submentale), submandibular triangle (trigonum submandibulare), carotid triangle (trigonum caroticum), and omotracheal triangle (trigonum omotracheale).
- The lateral triangle includes: the omotrapezoid triangle (trigonum omotrapezoideum) and omoclavicular triangle (trigonum omoclaviculare).
The level of the 6th cervical vertebra is easy to remember using the "Three Ps" rule: Passage of the larynx (into the trachea), Passage of the pharynx (into the esophagus), Pressing the artery (against the carotid tubercle).
Class and exam questions
Where is the carotid tubercle located and what is its purpose?
The carotid tubercle is the anterior tubercle of the transverse process of the sixth cervical vertebra. It is palpated laterally to the cricoid cartilage and serves as a landmark for compressing the common carotid artery in case of severe hemorrhage.
Where is the exit point of the sensory branches of the cervical plexus projected?
The exit point of the sensory branches of the cervical plexus (including the great auricular and transverse cervical nerves) is projected at the midpoint of the posterior border of the sternocleidomastoid muscle.
At what level is the thyrohyoid ligament located?
The thyrohyoid ligament (lig. thyrohyoideum) spans between the hyoid bone and the upper border of the thyroid cartilage. Topographically, this level corresponds to the lower part of the pharynx.
Which vertebrae correspond to the jugular notch of the sternum?
Skeletotopically, the jugular notch of the sternum corresponds to the intervertebral disc between the II and III thoracic vertebrae.
What else to study on this topic
- Boundaries and contents of the carotid triangle
- Topography of the submandibular triangle
- Muscles of the neck: superficial, intermediate, and deep
- Venous anastomoses of the neck and the jugular vein system
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