INTRODUCTION:
It is the triangular space of the side of the neck, situated in front of the sternocleidomastoid (SCM) muscle.

BOUNDARIES:

Anteriorly: Anterior midline of the neck.
Posteriorly: Anterior border of the SCM muscle.
Base: It is directed upwards form by the base of mandible and line joining the angle of the mandible to the mastoid process.
Apex: It is directed downwards, formed by suprasternal notch where two muscles unite.

ROOF: 

  • Skin.
  • Superficial fascia containing platysma muscle.
  • Investing layer of deep cervical fascia.

SUBDIVISIONS OF THE ANTERIOR TRIANGLE:

The Digastric muscle and Superior belly of Omohyoid muscle divide the anterior triangle into four smaller triangles as: 

1. Submental Triangle.
2. Digastric / Submandibular Triangle.
3. Carotid Triangle.
4. Muscular Triangle.

1. SUBMENTAL TRIANGLE:

BOUNDARIES:

On each side: Anterior belly of the digastric muscle.
Base: It is formed by the body of the hyoid bone.
Apex: It lies at the chin.

Floor: 

It is formed by Mylohyoid Muscles.

Roof: 

It is formed by:
A. Skin 
B. Superficial fascia containing-

  • Platysma
  • Cervical Branch of the facial nerve.
  • Anterior middle jugular vein 

C. Deep cervical fascia: Investing layer of deep cervical fascia.

Content: 
The submental triangle is unpaired. The contents are:
  • Anterior Jugular vein.
  • Sub-mental lymph nodes.

2. DIGASTRIC / SUBMANDIBULAR TRIANGLE:

BOUNDARIES:
Anteroinferior: Anterior belly of the digastric muscle.

Posteroinferiorly: Posterior belly of the digastric muscle. 

Base / Superiorly: It is formed by the base of mandible and line joining the angle of the mandible to the mastoid process.

Floor:

  • Anterior half by- Mylohyoid muscle.
  • Posterior half by-Hyoglossus muscle.
  • A small part by- Middle constrictor muscle of the pharynx.

Roof: 

It is formed by:

A. Skin 
B. Superficial fascia containing-

  • Platysma
  • Cervical Branch of the facial nerve.
  • Ascending branch of the anterior cutaneous nerve of the neck.

C. Deep cervical fascia: Investing layer of deep cervical fascia enclosing submandibular salivary gland.

Content: 

The submandibular triangle is paired. The contents are:

 1. Anterior Part of the Triangle:
  • Submandibular salivary gland.
  • Submandibular lymph node.
  • Facial artery and vein.
  • Submental artery.
  • Nerves: Mylohyoid and hypoglossal.
2. Posterior Part of the Triangle:
a) Superior structures:
  • Parotid gland.
  • External Carotid artery.
b) Deep structures:
  • Styloglossus.
  • Stylopharyngeus.
  • Styloid process.
  • Glossopharyngeal nerve.
  • Pharyngeal branch of the vagus nerve.
c) Deepest structures:
  • Internal Carotid artery.
  • Internal jugular vein.
  •  Vagus Nerve.

3. CAROTID TRIANGLE:

It is a most important subdivision of Anterior triangle and contains many vessels, nerves, and glands.

BOUNDARIES:

Anterosuperiorly: Posterior belly of the digastric muscle & Stylohyoid. 
Anteroinferior: Superior belly of the omohyoid.
Posteriorly: Anterior border of the sternocleidomastoid muscle.

Floor:

It is composed of the:
  • Hyoglossus.
  • Thyrohyoid.
  • Middle constrictor of the pharynx.
  • Inferior constrictor of the pharynx.

Roof: 

It is formed by:

A. Skin 
B. Superficial fascia containing-
  • Platysma
  • Cervical Branch of the facial nerve.
  • The transverse cutaneous nerve of the neck.
C. Deep cervical fascia: Investing layer of deep cervical fascia.

Content: 

1. Arteries:
  • Common carotid
  • Internal carotid
  • External carotid with its branches Superior thyroid, Lingual, Facial, Ascending pharyngeal, Occipital.
2. Vein:
  • Internal Jugular vein.
  • Common facial vein.
  • Lingual Vein.
  • Pharyngeal vein.
3. Nerves:
  • Vagus.
  • Superior laryngeal nerves.
  • Spinal Accessory.
  • Hypoglossal.
  • Ansa cervicalis.
4. Structures:
  • Larynx. 
  • Thyroid.
5. Deep cervical lymph nodes.
6. Carotid sheath.

4. MUSCULAR TRIANGLE:

It is situated on each side of the midline of the front of the neck.

BOUNDARIES:

Anteriorly: Anterior midline of neck from the hyoid bone to the sternum.
Posterosuperior: Superior belly of the omohyoid muscle.
Posteroinferiorly: Anterior border of the sternocleidomastoid muscle.

Floor:

It is formed by-
  • Sternohyoid.
  • Sternothyroid.

Roof:

  • Skin.
  • Superficial fascia with platysma.
  • Deep cervical fascia.

Content:

Infrahyoid muscles are the chief content. They are:
  • Sternohyoid.
  • Sternothyroid.
  • Thyrohyoid.
  • Omohyoid.