Anterior triangle of the neck

Anterior triangle of the neck
Written by : Hisham Saleem
Dr.Zuhair Fadhl
It is a large area infront of the neck.
Bounded by the lower border of the mandible, & lying between the two
sternocleidomastoids.
Roof: Investing layer of deep cervical fascia.
Beneath it there is a group of longitudinal strap muscles, that extends from the
mandible to the sternum:-
* Above hyoid bone: - Geniohyoid muscle
- Myelohyoid muscle
* Below the hyoid bone:
- Superficial (1 st ) layer: Sternohyoid muscle
Omohyoid muscle
- Deep ( 2 nd ) layer: Thyro-hyoid muscle
Sternothyroid muscle
Subdivisions of the anterior triangle
A) Submental triangle:
Bounded by : the 2 bellies of digastric & the hyoid bone.
Floor formed by : the myelohyoid muscle
Occupied by : lymphnodes.
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B) Digastric (Submandibular) triangle:
Written by : Hisham Saleem
Dr.Zuhair Fadhl
Bounded by : the ant. belly of the digastric muscle, stylohyoid muscle & the lower
border of the mandible.
Floor formed by: myelohyoid & hyoglossus muscles.
Occupied by: Submandibular lymphnodes & Submandibular salivary glands.
C) Carotid triangle:
Bounded by: the sternocleidomastoid muscle, posterior belly of digastric & the
superior belly of omohyoid muscles.
Floor formed by: Anteriorly; formed by the hyoglossus & thyrohyoid muscles
Posteriorly; by middle & inferior constrictor muscles.
Occupied by: the vertical nervovascular bundle of the neck, covered by the
sternocleidomastoid muscle.
D) Muscular triangle:
Bounded by: the sternocleidomastoid, superior belly of omohyoid & median plane
(mid line).
Occupied by: the infra hyoid muscles.
Supra Hyoid muscles ( muscles form the floor of
mouth)
1) Myelohyoid
2) Geniohyoid muscle
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Infra Hyoid muscles
Sternohyoid muscle:
Written by : Hisham Saleem
Dr.Zuhair Fadhl
Flat strap muscle situated close to each other above but diverge from each other
below.
Origin: from lower border of hyoid bone
Insertion: to the back of sterno clavicular joint & adjoining parts of manubrium &
clavicle.
Nerve supply: Branch from ansa cervicalis C1,2,3 enter through its lower end &
supply it segmentally.
Tendinous insections may be present which indicate segmental origin of the muscle.
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Omohyoid muscle:
Long muscle formed of 2 bellies and intermediate tendon.
Written by : Hisham Saleem
Dr.Zuhair Fadhl
Superior belly:
Origin: from lateral part of the inferior border of hyoid bone, descends obliquely
downward passing beneath the sternomastiod muscle & over the carotid
sheath.
Insertion : muscle fibers are replaced by flat intermediate tendon.
Inferior belly:
Origin: attached to the transverse scapular ligament & upperborder of the
scapula. Situated horizontal to the upper border of the clavicle.
Insertion: Intermediate tendon, which is bound down to the clavicle by facial sling
(from deep cervical fascia).
Nerve supply: segmentally by C1,2,3 by the ansa cervicalis.
Action: when the head is rotated to one side, the opposite omohyoid is straightened &
can exert a more downward pull on the hyoid bone.
Thyro hyoid muscle:
Flat broad strap-like muscle, lies beneath sternohyoid & omohyoid muscles.
Origin: greater horn of hyoid bone.
Insertion: oblique line of thyroid cartilage, end to end with sterno thyroid muscle.
Nerve supply: branch of hypoglossal nerve carries C1 fibers.
Sterno thyroid muscle:
Broad flat muscle.
Origin: oblique line of thyroid cartilage.
Insertion: posterior surface of manubrium below Sternohyoid & from manubrium
to first costal cartilage.
Nerve supply: ansa cervicalis C2, 3.(C1 to thyrohyoid)
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Action of infrahyoid muscles.
Written by : Hisham Saleem
Dr.Zuhair Fadhl
Depression of the larynx: sternothyroid acts directly on thyroid cartilage, the
others indirectly via hyoid bone.
Opponent of the elevators of the larynx (myelohyoid, palatopharyngeus,
stylopharyngeus & salpingopharyngeus).
Prevent ascent of the hyoid bone when the digastric muscle is in action.
Digastric muscle:
Composed of 2 bellies & an intermediate tendon.
It is formed by fusion of component of 1st & 2nd pharyngeal arches.
Anterior belly: a fleshy belly
Origin: from digastric notch on the medial surface of the mandible.
Insertion: it tapers down to the intermediate tendon.
Posterior belly:
Origin: medial surface of mastoid process.
Insertion: Intermediate tendon.
Intermediate tendon:
Held by fibrous sling to the lesser cornu of the hyoid bone, which Is lubricated by
synovial sheath.
Nerve supply: Anterior belly: myelohyoid nerve (V).
Posterior belly: facial nerve (VII).
Action: depresses & retracts the chin.
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