Posterior Triangle and Suboccipital Region

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Posterior Triangle and Suboccipital Region

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Posterior Triangle and Suboccipital Region

Bony landmarks:

  • Superior nuchal line of skull

  • posterior tubercle of atlas (C1 vertebra)

  • spinous process of axis (C2 vertebra)

Posterior Triangle


  • 1) Trapezius

Function: extends head if scapula is fixed, raises the arm, elbow forward.

Innervation: spinal accessory nerve (CN XI)

  • 2) Sternocleidomastoid

Origins: medial 1/3 of clavicle and front of manubrium.

Insertion: mastoid process.

Function: turns and tilts the head, (and accessory muscle of inspiration).

Innervation: spinal accessory nerve (CN XI)

  • 3) Middle Third of Clavicle

  • 4) Apex: Superior Nuchal line of skull

Muscles in the Posterior Triangle:

  • Platysma: Most superficial muscle in the posterior triangle. Think of it as the "Roof" of the posterior triangle.

    • Functions:

      • Muscles of facial expression

      • Helps depress jaw

      • Aids circulation by relieving pressure on veins

    • Innervation: cervical branch of facial nerve.

  • Omohyoid

Muscles forming the floor of the posterior triangle:






Splenius capitis

Vertebral spinous processes of C3-T5 (part of erector spinae system)

Superior nuchal line

extends and rotates head

Upper cervical dorsal rami

Levaltor scapulae

Transverse processes (C1-C4)

Medial scapula

Bends neck when scapula fixed; elevates and rotates scapula.

Ventral ramus (C3-C4) and dorsal scapular nerve.

Middle Scalene

Transverse processes C1-C7

Upper surface of first rib (behind subclavian groove)

Bends neck forward and to the side. When they both act together, they fix the neck or if the neck is fixed, they elevate the ribs.


Posterior Scalene

Transverse process of C5-C6

Lateral surface of second rib

Same as middle scalene


Vasculature of Posterior Triangle:

External jugular vein

  • Comes from a union of the posterior auricular and retromandibular veins and then crosses the sternocleidomastoid and drains into the subclavian vein. One can distinctly see it pulsate especially under high venous pressure.


Bear in mind that there is variability in where these arteries arise from.

  • Transverse cervical artery: comes from the thyrocervical trunk OR as a separate trunk with the suprascapular artery and supplies the trapezius and levator scapulae. Note that the transverse cervical artery does not run with the transverse cervical nerve. The nerve proceeds anteriorly whereas the artery proceeds posteriorly.

  • Third part of subclavian artery:The longest portion of the subclavian artery. Supplies blood to the Upper limb.

  • Suprascapular artery: Comes from the thyrocervical trunk OR from a common trunk with the transverse cervical artery. Supplies Shoulder.

  • Dorsal scapular artery: Comes directly from the subclavian artery (70%) OR the thyrocervical trunk (30%) and supplies the Medial shoulder.

Innvervation of Posterior Triangle

  • Sensory: From Cervical Plexus

  • Motor: Spinal accessory CN XI

Think of the locations of the nerves as if they were hands on a clock...

    • Great auricular n. (12:00):supplies innervation to the skin over the parotid gland, the posterior aspect of auricle and an area of skin from mandible to mastoid process, runs superficial to sternocleidomastoid and in an anteriosuperior direction.

    • Lesser occipital n. (1:00): Supplies the skin of neck and scalp posteriosuperior to auricle, and runs posterior to sternocleidomastoid.

    • Accessory n. (4:00): Supplies SCM from deep aspect, then passes posterior-inferiorly to supply the trapezius.

    • Supraclavicular n. (6:00): Supplies skin of upper anterior chest wall and adjacent shoulder.

    • Transverse cervical n. (9:00): Supplies skin of anterior neck

Note: the clock analogy is of the left side. It would be backwards from the other side.

All of these nerves come out from behind the SCM. You can locate them by palpating along the SC< until you reach a point that hurts when pressure is applied. You can think of GLAST (sounds like "blast") if that helps you remember it...

Highlights From the Suboccipital Region:

The four muscles of this triangle serve to anchor the atlas and axis to each other and to the skull.

Deep Muscles

Nerve Supply


Obliquus capitis inferior

Suboccipital nerve

Ipsilaterally rotates C1 with respect to C2

Obliquus capitis superior


extends the head

rectus capitis posterior major


extend the head backwards, act as fine-tuners, proprioceptors

rectus capitis posterior minor



You should know insertions and origins for all of the deep muscles, as these form the corners of the suboccipital triangle.

Other Important Information About the Suboccipital Triangle

In addition to the contents of the suboccipital triangle, know these too:

  • 1) Vertebral artery - compression of this artery due to prolonged rotation can cause dizziness.

  • 2) Suboccipital nerve (dorsal rami of C1)

  • 3) Greater Occipital nerve: Closely associated with this triangle. It emerges below the inferior border (obliquus capitis inferior) and runs superficially to this space to innervate the posterior scalp.

Anterior Triangles of Neck and Cervical Viscera

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The Anterior triangle (Netter 24)


  • Sternocleidomastoid

  • Anterior midline of neck

  • Inferior edge of mandible


  • Omohyoid m.

  • Digastric m.

  • Hyoid bone

Sub-Triangles of the Anterior Triangle

submandibular ∆

Submandibular Triangle:

  • mandible (sup.)

  • digastric (ant.-inf.and post.-inf.)

Submental ∆

Submental Triangle(unpaired)

  • Anterior bellies of digastric (lateral)

  • mandible (anterior)

Muscular ∆

Muscular Triangle

  • sterocleidomastoid (posterior)

  • superior belly of omohyoid (posterior - superior)

  • midline; hyoid bone (superior)

Carotid ∆

Carotid Triangle

  • posterior belly of digastric (anterior - superior)

  • sternocleidomastoid (posterior)

  • sup. Belly of omohyoid (anterior - inferior)

Hyoid Bone

Hyoid bone (Moore T-8.3)

Characteristics: U-shaped Portions:

  • Body

  • Greater horn

  • Lesser horn


  • Raises/lowers larynx

  • Provides stable platform for the:

    • tongue

    • suprahyoid m.’s (primary depressors of mandible)


Superior Attachments

Inferior Attachments

Other Attachments

Suprahyoid Muscles

Infrahyoid Muscles

Middle Pharyngeal Constrictor

Other m's of mouth & tongue

Thyrohyoid Membrane

Suprahyoid Muscles

Suprahyoid Muscles (Netter 25)

Digastric Muscles Stylohyoid Mylohyoid Geniohyoid: deeper Table 8.3 in Moore is good reference. However geniohyoid muscle is mislabeled.

All suprahyoid muscles elevate the larynx and inferior pharynx and all elevate the floor of mouth to propel contents of mouth into pharynx. All can stabilize hyoid during speech and swallowing.


Digastric Muscle

Stylohyoid Muscle

Mylohyoid Muscle

Geniohyoid Muscle


2 bellies:

  • posterior belly: mastoid notch of temporal bone

  • anterior belly: digastric fossa of posterior mandible

styloid process of temporal bone

mylohyoid line of mandible

inferior mental spine of mandible


intermediate tendon to hyoid bone

body of hyoid bone

onto body of hyoid, and onto itself on midline

body of hyoid


depresses mandible and elevates hyoid

elevates & retracts hyoid

elevates and protracts hyoid

protracts hyoid


2 bellies:

  • posterior belly: facial nerve

  • anterior belly: nerve to the mylohyoid (V3)

cervical branch of Facial n.

mylohyoid n. (V3)


Muscular Triangle and Infrahyoid Muscles

(Netter 25A, 25B; Moore 8.12)

General observations on the infrahyoid muscles:

Made for mobility of larynx and pharynx

Actions depend on actions of the suprahyoid muscles

Help co-ordinate movements of the head, neck, tongue, larynx and pharynx They are flexors of the neck in conjunction with the suprahyoid muscles

Contraction of the infrahyoid and suprahyoid muscles simultaneously:

  • with jaw fixed → fixes hyoid bone, provides firm base for tongue movement (speech)

  • with jaw mobile → depresses the jaw (with suprahyoids and platysma)







manubrium and medial clavicle

posterior surface of manubrium

thyroid cartilage

superior scapula (just medial to suprascapular notch)


body of hyoid

thyroid cartilage

body and greater horn of hyoid

hyoid bone


depresses hyoid, e.g., after elevation during swallowing stabilizes hyoid, e.g., during opening of mouth

depresses hyoid (indirectly) depresses thyroid cartilage (directly) depresses thyroid cartilage, i.e., lengthens the vocal cords

depresses hyoid OR elevates larynx. Opposes larynx to epiglottis, i.e., shortens the vocal cords

depresses & retracts hyoid draws hyoid laterally when turning head


C1, C2, and C3

C2 and C3

C1, branch from fibers running with the hypoglossal nerve

C1, C2, and C3.



deep to sternohyoid

deep to sternohyoid

Ansa Cervicalis: innervation of infrahyoid muscles (Netter 27, 28A, 28B)

Comprised of branches of C1, C2, and C3

Superior root: runs with hypoglossal n.

Inferior root: direct branch of cervical plexus

Not a true loop: no recurring fibers: two descending branches join, forming a "Y". Supplies infrahyoid muscles more superior roots supply more superior muscles (and vice versa)

does not supply the thyrohyoid)

Carotid Triangle

(Netter 24)

Separated from the muscular triangle by the superior belly of the omohyoid muscle

Bounded by:

  • Sternocleidomastoid

  • Posterior belly of digastric

  • Superior belly of omohyoid

Contents of carotid triangle: (Netter 27, 28A, 28B)

  • Within Carotid sheath

common carotid artery, internal jugular vein, vagus nerve, retromandibular vein, facial vein, superior and middle thyroid veins, ansa cervicalis; superior root (sometimes)

  • Outside Carotid Sheath: (Netter 28A, 28B)

hypoglossal nerve, spinal accessory nerve, ansa cervicalis, branches of vagus nerve: internal and external branches of superior laryngeal nerve, recurrent laryngeal n., branches of external carotid a.

Branches of the common carotid artery

(Netter 30A, 30B)

  • Internal carotid artery

no branches in the neck; supplies structures in skull

  • External carotid artery

8 branches; supplies structures external to skull

Branches of External Carotid Artery:

(Netter 30A, 30B)

Superior thyroid artery: to the thyroid gland gives off superior laryngeal artery runs through thyrohyoid membrane runs with internal laryngeal nerve

Ascending pharyngeal artery: small & deep to posteriolateral pharynx

Lingual artery: runs behind posterior belly of the digastricsupplies the tongue

Facial artery: supplies face may be a common linguofacial trunk pulse palpable crossing mandible

Occipital artery:supplies posterior scalp + SCM runs posteriorly along post. belly of digastric,to sternocleidomastoid

Posterior Auricular artery: branch level: superior border of posterior belly of digastric supplies the parotid gland, ear, scalp and structures in temporal bone

Maxillary artery:supplies maxillary region

Superficial temporal artery: supplies temporalis muscle, etc

Transverse facial artery

Other contents of the carotid sheath

(Moore 8.14)

  • Carotid body

    • location: bifurcation of common carotid a.

    • innervation: glossopharyngeal nerve

    • responds to increasing pCO2 or decreasing p02

  • Carotid sinus

    • dilation of proximal internal carotid artery

    • innervation: glossopharyngeal nerve

    • responds to decreasing blood pressure

Root of the Neck: Junction of the Neck and Thorax

(Netter 29A, 29B; G.D fig 7.62)

Boundaries (Includes superior thoracic aperture)

Contents: Arteries, veins, lymphatics , nerves, muscles

Arteries of Root of Neck (Netter 29A, 29B; Moore fig 8.19)
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