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Anterior Triangle of the Neck and Submandibular Region
I.
Muscles
A. infrahyoid muscles – the strap muscles are named by their origins and insertions
1. sternohyoid muscle #1
a. arises within the thorax behind the manubrium
b. inserts into the inferior border of the body of the hyoid bone
c. draws the hyoid bone inferiorly
d. innervation – ansa cervicalis (C1, 2, & 3)
2. sternothyroid #2
a. arises from posterior manubrium below the origin of the preceding muscle
b. inserts into the oblique line on the lamina of the thyroid cartilage
c. draws the thyroid cartilage caudalward
d. innervation- ansa cervicalis (C1, 2, & 3)
3. thyrohyoid muscle #3
a. arises from the oblique line of the lamina of the thyroid cartilage
b. inserts on the inferior border of the greater cornu of the hyoid bone
c. draws the thyroid cartilage downward
d. innervation – branches of C1 & 2 via hypoglossal nerve
4. omohyoid muscle #4
a. arises superior border near the suprascapular notch
b. inserts into inferior border of the hyoid bone just lateral to the sternohyoid
c. draws the hyoid bone downward
d. it is composed of two bellies that are formed by its mid-portion being bound
down to the clavicle by a fibrous expansion
(1) inferior belly – from origin to the fibrous expansion; changes direction
behind the sternocleidomastoid
(2) superior belly – from fibrous expansion to its insertion on hyoid bone
e. innervation – ansa cervicalis (C1, 2, 3)
B. suprahyoid muscles
1. digastric muscle #1 – has two bellies joined by an intermediate tendon which
passes through the stylohyoid muscle and held in place by a fibrous loop
attached to the upper part of the body of the hyoid bone
a. inferior belly
(1) originates from medial aspect of the mastoid bone
(2) innervation – facial nerve (Cr. N. VII)
b superior belly
(1) inserts into the symphysis menti on the internal surface of the mandible
(2) innervation – nerve to the myelohyoid off the inferior alveolar nerve,
which a branch of the trigeminal nerve (Cr. N. V)
c. their action is to raise the hyoid bone and assist in opening the jaws
2. stylohyoid muscle #2
a. arises from the styloid process
b. inserts into the body of the hyoid bone
c. draws the hyoid bone posteriorly and superiorly
d. innervation – a branch of the facial nerve (Cr. N. VII)
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3. myelohyoid muscle #3
a. directly above the anterior bellies of the digastrics and both form the floor of
the mouth as they join together in the midline by a median fibrous raphe
b. arises from the myelohyoid line of the mandible
c. inserts into the body of the hyoid bone
d. raises the hyoid bone and tongue
e. innervation – nerve to the myelohyoid (Cr. N. V)
4. geniohyoid muscle #4
a. arises from inferior mental spine on inner surface of the symphysis menti
directly above the myelohyoid in the midline
b. inserts into the anterior surface of the hyoid bone
c. draws the hyoid bone and tongue forward
d. innervation – a branch of C1 via the hypoglossal nerve
II.
Triangles of the neck
A. posterior triangle – bounded by
1. anterior - sternocleidomastoid muscle
2. posterior – anterior margin of the trapezius muscle
3. base – middle third of the clavicle
B. anterior triangle bounded by
1. base – lower margin of the mandible
2. anterior – midline of the neck
3. posterior – sternocleidomastoid muscle
C. the anterior triangle is subdivided into four smaller triangles
1. digastric or submandibular triangle bounded by
a. two bellies of the digastric muscle
b. lower border of the mandible
2. carotid triangle bounded by
a. posterior belly of the digastric muscle
b. superior belly of the omohyoid muscle
c. anterior margin of the sternocleidomastoid muscle
3. muscular triangle bounded by
a. midline of the neck
b. anterior margin of the sternocleidomastoid muscle
c. superior belly of the omohyoid muscle
4. submental triangle – the only unpaired triangle bounded by
a. two anterior bellies of the digastric muscles
b. hyoid bone
D. submandibular triangle and its contents
1. floor – myelohyoid and hyoglossus muscles
2. submandibular gland – major salivary gland
a. almost fills the triangle
b. lays below and in front of the angle of the mandible
c. divided into a large superficial part and a smaller deep part
(1) superficial part lays on the inferior surface of the myelohyoid muscle,
wraps around the posterior free edge of that muscle becoming deep
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3.
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III.
(a) deep part lays between the myelohyoid and hyoglossus muscles
(2) submandibular duct (Wharton's duct) arises from the deep part of
the gland, passes forward between the myelohyoid and hyoglossus
muscles to open under the tongue through an opening of a small
papilla, the sublingual caruncle
(a) at the anterior border of the hyoglossus muscle it is crossed on its
lateral side by the lingual nerve; the lingual nerve passes beneath
duct and its terminal fibers ascend into the tongue on the medial
side of the duct
submandibular lymph nodes lay the gland and between it and the lower
border of the mandible
vessels
a. facial artery – a branch of the external carotid artery
(1) arises in the carotid triangle medial to the ramus of the mandible and
passes medial to the digastric and stylohyoid muscles; it then passes
forward in a groove on the posterior surface of the submandibular
gland, winds under the border of the mandible at the anterior edge of
the masseter muscle to enter the face
(2) its terminal branch is the submental artery
facial vein
(1) in the face, it accompanies and is posterior the facial artery; it curves under
the mandible on the anterior border of the masseter muscle, draining into
the internal jugular vein
relationships in the submandibular triangle
a. myelohyoid nerve is on the superficial surface of the myelohyoid muscle
and deep to the submandibular gland sending branches to the
(1) myelohyoid muscle
(2) anterior belly of the digastric muscle
b. intermediate tendon of the digastric muscle on the surface of the
hyoglossus muscle
c. hypoglossal nerve (Cr. N. XII) runs forward on the hyoglossus muscle and
deep to the submandibular gland
(1) passes between the myelohyoid and hyoglossus muscles
d. lingual nerve (Cr. N V) also passes between the myelohyoid and
hyoglossus muscles
e. lingual artery (off the external carotid artery) passes deep to the
hyoglossus muscle
Common carotid artery
A. in the carotid sheath with the internal jugular vein and vagus nerve (Cr. N X)
B. at the level of the upper border of the thyroid cartilage it divides into the internal
and external carotid arteries
C. at the bifurcation of the carotid artery are the
1. carotid body – deep in the bifurcation
a. has chemoreceptors for oxygen levels in blood and the information is
transmitted to the medulla via the glossopharyngeal and vagus nerves
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2. carotid sinus – slight dilation at the terminal part of common carotid artery
a. has end organs that sense blood pressure via glossopharyngeal nerve
D. branches of the internal and external carotid arteries
1. internal carotid artery has no branches in the neck
2. external carotid artery branches in the neck
a. superior thyroid artery has four branches but the largest is the
(1) superior laryngeal artery – accompanies the internal branch of the
superior laryngeal nerve through the thyrohyoid membrane
b. lingual artery – comes off above the preceding artery and passes deep to
the hyoglossus muscle to supply the tongue
c. facial artery comes off superior to the preceding artery
(1) passes to the submandibular gland or even in it to supply the face
(2) in the neck it gives off the following branches
(a) glandular
(b) ascending palatine
(b) tonsillar
(d) submental
d. ascending pharyngeal artery
(1) 1st artery to come off the posterior surface of the external carotid artery
e. occipital artery
(1) comes off above the preceding artery and opposite the facial artery.
(2) it courses upwards and medial to the hypoglossal nerve and grooves
the medial surface of the process
(3) gives off muscular branches along the way and terminates in the
posterior scalp lateral to the greater occipital nerve (dorsal ramus; C2)
V.
Veins in the upper neck
A. venous drainage of the superficial structures of the head and neck
1. posterior auricular vein
2. retromandibular vein formed by the junction of the
a. superficial temporal vein
b. maxillary vein
3. facial vein
4. external jugular vein
a. formed by the junction of the
(1) posterior auricular vein
(2) posterior branch of the retromandibular vein
b. descends across the SCM muscle to empty into the subclavian vein
5. venous drainage of the deep structures of the neck
1. internal jugular vein
a. lies in the carotid sheath with the carotid artery and vagus nerve
b. arises from sinuses within the cranial cavity
c. descends from the posterior compartment of the jugular foramen then
moves from posterior to lateral in relation to the carotid artery
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VI.
Lymphatic drainage of the head and neck
A. facial nodes accompany the facial vessels in the head, but most lymph vessels
flow relatively vertical to the nodes at the junction of the head and neck.
B. nodes at the junction of the head and neck:
1. submental
2. submandibular – receive lymph from a wide area including the deep and
superficial face
3. superficial parotid
4. mastoid
5. occipital
C. superficial cervical nodes – external jugular nodes
D. cervical nodes located deep to investing fascia
1. infrahyoid
2. prelaryngeal
3. pretracheal
4. paratracheal
5. accessory
6. transverse cervical
7. deep parotid
8. retropharyngeal
E. final common pathway for head and neck lymph
1. superior deep cervical nodes – form a chain along the carotid sheath near the
internal jugular vein
a. jugulodigastric
b. juguloomohyoid
2. inferior deep cervical nodes
3. efferent vessels from the deep cervical nodes drain into a jugular lymph trunk
a. on the left drainage is into the thoracic duct
b. on the right drainage is into the right lymphatic trunk
VII.
Nerves
A. cranial nerves in the anterior triangle of the neck
1. trigeminal nerve (Cr. N. 5 / Cr. N V) – nerve to the myelohyoid, which also
supplies the anterior belly of the digastric muscle
2. facial nerve (Cr. N. 7 / Cr. N. VII) – the cervical branch of the facial nerve
supplies the platysma muscle. The main trunk of the of the facial nerve also
gives fibers to the stylohyoid and posterior belly of the digastric muscles.
3. glossopharyngeal nerve (Cr. N. 9 / Cr. N. IX) – supplies the carotid sinus
(blood pressure sensitive) with afferent fibers via the nerve of Hering.
4. vagus nerve (Cr. N. 10 / Cr. N. X)
a. the main trunk passes through the neck inside the carotid sheath with the
internal jugular vein and carotid artery
(1) superior and inferior cervical cardiac nerves – visceral branches of
the cardiac plexuses
(2) superior laryngeal nerve
(a) external branch – innervates the cricothyroid muscle
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(b) internal branch
i. passes through the thyrohyoid membrane
ii. sensory to the laryngeal mucosa above the true vocal folds
iii. important for the cough reflex
(3) pharyngeal branch goes between carotid arteries. Communicates with
the glossopharyngeal nerve and accessory nerve to form the
pharyngeal plexus. This plexus contains motor fibers to pharyngeal
muscles (except the tensor veli palatine, Cr. N 5) and sensory to
pharyngeal mucous membranes.
(4) recurrent (inferior) laryngeal branch – lays in a groove between
trachea and esophagus. Supplies vocal muscles and mucous membrane
below the true vocal folds.
5. accessory nerve (Cr. N. 11 / Cr. N. XI)
a. spinal part
(1) enters the deep surface of the SCM muscle high in the neck and
supplies that muscle
(2) then crosses the posterior triangle of the neck to supply the
trapezius muscle
b. cranial part
(1) integrated into the pharyngeal plexus
(2) supplies motor axons to the following pharyngeal muscles
(a) muscularis uvulae
(b) levator veli palatini
(c) pharyngeal constrictors
6. hypoglossal nerve (Cr. N 12 / Cr. N. XII)
a. crosses external to both carotid arteries
c. goes deep to the myelohyoid muscles
c. carries branches from C1& 2 to the ansa cervicalis in the cervical plexus
B. ansa cervicalis
1. innervation to the infrahyoid muscles
2. forms a loop on anterior surface of the internal jugular vein by connecting
branches of the hypoglossal and cervical nerves
a. descendens hypoglossi or superior root
(1) fibers from C1 & 2 run with the hypoglossal nerve
(2) C1 & 2 fibers directly innervate thyrohyoid and geniohyoid muscles
(3) innervates the superior belly of omohyoid muscle via ansa cervicalis
b. descendens cervicalis or inferior root
(1) fibers from C2 & 3
(2) supplies sternohyoid, sternothyroid, and inferior belly of omohyoid
muscles
C. cervical portion of the sympathetic system
1. superior cervical ganglion does or supplies the following
a. internal carotid nerve and plexus
b. superior cardiac nerve
c. communicates with Cr. Ns 9, 10, & 11
d. has gray communicating rami to C1, 2, 3, & 4
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e. pharyngeal plexus
f. branches to the external carotid artery
2. middle cervical ganglions does or supplies the following
a. middle cervical cardiac nerves
b. gray communicating rami to C5 & 6
c. if it is in a lower position it has been referred to as the thyroid or
vertebral ganglion
3. inferior cervical ganglion does or supplies the following
a. inferior cardiac nerve
b. gray communicating rami to C6, 7, & 8
c. may fuse with the 1st thoracic ganglion to form the stellate ganglion
d. vertebral nerve – accompanies the vertebral artery
VIII. Thyroid gland
A. an endocrine gland usually shaped like the letter "H": weighs about 30 grams
1. two lateral lobes extending from the oblique line of the thyroid cartilage
down to the level of the 5th or 6th tracheal ring
2. isthmus connects lower thirds of lateral lobes
a. usually covers the 2nd and 3rd tracheal rings
3. pyramidal lobe may be present, extending upwards from the isthmus
B. blood supply
a. superior thyroid artery - off the external carotid artery
b. inferior thyroid artery – off thyrocervical trunk of subclavian artery
C. parathyroid glands – usually there are two superior and inferior on the dorsal
side of the thyroid gland
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