Boundaries

• Anterior → Anterior median plane of the neck.
• Posterior → Anterior border of sternocleidomastoid.
• Base → Base of mandible and a line joining the angle of mandible to the mastoid process, superiorly.
• Apex → Directed downward; formed by the meeting point of:
  • Anterior border of sternocleidomastoid muscle.
  • Anterior median line.

Roof

1. Skin.
2. Superficial fascia with platysma.
3. Investing layer of deep cervical fascia.

Subdivisions

The anterior triangle is subdivided by the digastric muscle and superior belly of omohyoid into:

1. Submental triangle.
2. Digastric triangle.
3. Carotid triangle.
4. Muscular triangle.

Boundaries

• Apex → Lower border of symphysis menti or chin.
• Base → Body of hyoid bone.
• On each side → Anterior bellies of digastric muscles.
• Floor → Mylohyoid muscle and median raphe extending from symphysis menti to body of hyoid bone.
• Roof → Investing layer of deep cervical fascia.

Contents

1. Two to four small submental lymph nodes.
2. Small submental veins → join to form the anterior jugular veins.

Submental Lymph Nodes

• Situated in the superficial fascia between the anterior bellies of the digastric muscles.
• They drain:
  1. Superficial tissues below the chin.
  2. Central part of the lower lip.
  3. Adjoining gums.
  4. Anterior part of the floor of the mouth.
  5. Tip of the tongue.
• Their efferents pass to the submandibular nodes.

Boundaries

• Anteroinferiorly → Anterior belly of digastric.
• Posteroinferiorly → Posterior belly of digastric and stylohyoid muscle.
• Superiorly / Base → Base of mandible and a line joining:
  • Angle of mandible.
  • Mastoid process.
• Apex → Intermediate tendon of digastric muscle.

Floor

1. Mylohyoid muscle.
2. Hyoglossus muscle.
3. Middle constrictor muscle of the pharynx.

Roof

The roof is formed by:

1. Skin.
2. Superficial fascia containing:
   • Platysma.
   • Cervical branch of facial nerve.
   • Ascending branch of transverse/anterior cutaneous nerve of the neck.
3. Deep fascia → splits to enclose the submandibular salivary gland.

Division

The stylomandibular ligament divides the triangle into:

1. Anterior part.
2. Posterior part.

Contents

Anterior Part of the Triangle

Structures superficial to mylohyoid

1. Superficial part of the submandibular salivary gland.
2. Facial vein.
3. Submandibular lymph nodes.
4. Facial artery → is deep to it.
5. Submental artery.
6. Mylohyoid nerve and vessels.
7. Hypoglossal nerve.

Posterior Part of the Triangle

1. Superficial Structures

1. Lower part of the parotid gland.
2. External carotid artery.

2. Deep Structures

Structures passing between the external and internal carotid arteries:

• Styloglossus muscle.
• Stylopharyngeus muscle.
• Glossopharyngeal (IX) nerve.
• Pharyngeal branch of vagus nerve.
• Styloid process.
• A part of the parotid gland.

3. Deepest Structures

• Internal carotid artery.
• Internal jugular vein.
• Vagus nerve.

Boundaries

• Anterosuperiorly → Posterior belly of digastric muscle and stylohyoid.
• Anteroinferiorly → Superior belly of omohyoid.
• Posteriorly → Anterior border of sternocleidomastoid muscle.

Roof

1. Skin.
2. Superficial fascia containing:
   • Platysma.
   • Cervical branch of facial nerve.
   • Transverse cervical nerve of the neck.
3. Investing layer of deep cervical fascia.

Floor

1. Middle constrictor of pharynx.
2. Inferior constrictor of pharynx.
3. Thyrohyoid membrane.

Contents

Arteries

1. Carotid arteries:
   • Common.
   • Internal.
   • External.
2. Carotid sinus and carotid body.
3. Superior thyroid artery.
4. Lingual artery.
5. Facial artery.
6. Ascending pharyngeal artery.
7. Occipital artery.

Veins

1. Internal jugular vein.
2. Common facial vein → drains into the internal jugular vein.
3. Pharyngeal vein → usually ends in the internal jugular vein.
4. Lingual vein → usually terminates in the internal jugular vein.

Nerves

1. Vagus nerve.
2. Spinal accessory nerve.
3. Hypoglossal nerve:
   • Gives the superior root of ansa cervicalis / descendens hypoglossi.
   • Gives another branch to the thyrohyoid.
4. Superior laryngeal branch of vagus:
   • Divides into external and internal laryngeal nerves.
5. Sympathetic chain.
6. Carotid sheath with its contents.

Boundaries

• Anteriorly → Anterior median line of neck from hyoid bone to sternum.
• Posterosuperiorly → Superior belly of omohyoid muscle.
• Posteroinferiorly → Lower part of anterior border of sternocleidomastoid muscle.
• Floor → Pretracheal fascia, thyroid and cricoid cartilages, and trachea.
• Roof → Investing layer of deep cervical fascia.

Contents

• The infrahyoid muscles are the chief contents of the triangle.
• These muscles may also be regarded arbitrarily as forming the floor of the triangle.

Peculiarities of Infrahyoid Muscles

1. Arranged in two layers:
   • Superficial → sternohyoid and omohyoid.
   • Deep → sternothyroid and thyrohyoid.
2. Supplied by the ventral rami of C1, C2 and C3 spinal nerves.
3. Because of their attachment to the hyoid bone and thyroid cartilage, they move these structures.
4. Sternohyoid, superior belly of omohyoid and sternothyroid lie superficial to the lateral/superficial convex surface of the thyroid gland.

Formation

It is formed by a superior root and an inferior root.

1. Superior Root / Descendens Hypoglossi

• It is the continuation of the descending branch of the hypoglossal nerve.
• Its fibres are derived from the C1 nerve.
• The root descends over:
  • Internal carotid artery.
  • Common carotid artery.

2. Inferior Root / Descendens Cervicalis

• Derived from C2 and C3 spinal nerves.
• As it descends:
  • Winds around the internal jugular vein.
  • Continues anteroinferiorly.
  • Joins the superior root in front of the common carotid artery.
• Both roots join to form the ansa cervicalis.

Distribution

1. Superior root → Superior belly of omohyoid.
2. Ansa cervicalis → Sternohyoid and sternothyroid.
3. Inferior root → Inferior belly of omohyoid.