1. Triangles of the neck Suboccipital Anterior Posterior
HEAD and NECK -- 2
Triangles of the neck
Suboccipital
Anterior
Posterior

2. Triangle
The suboccipital muscles are a group of muscles defined by their location to the occiput.
Suboccipital muscles are located below the occipital bone.
These are four paired muscles on the underside of the occipital bone; the two straight muscles (rectus) and the two oblique muscles (obliquus).

3. They are innervated by the suboccipital nerve.
Triangle
The muscles are named
Rectus capitis posterior major goes from the spinous process of the axis (C2) to the occipital bone.
Rectus capitis posterior minor goes from the middle of the posterior arch of the atlas to the occipit.
Obliquus capitis superior goes from the transverse process of the atlas to the occiput.
Obliquus capitis inferior goes from the spine of the axis vertebra to the transverse process of the atlas.
They are innervated by the suboccipital nerve.

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8. The suboccipital triangle
is a region of the neck bounded by the following three muscles of the suboccipital group of muscles:
Rectus capitis posterior major - above and medially
Obliquus capitis superior - above and laterally
Obliquus capitis inferior - below and laterally
The floor is formed by the posterior atlantooccipital membrane, and the posterior arch of the atlas.
In the deep groove on the upper surface of the posterior arch of the atlas are the vertebral artery and the first cervical or suboccipital nerve

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10. THE ANTERIOR TRIANGLES
The anterior triangle of the neck is an anatomical division created by the muscles of the head and neck. It is used clinically to locate structures that pass through the neck.
In this region are two major triangles which are separated by Sternocleidomastoid muscle. These are Anterior and Posterior triangles
(It is important to note that all triangles mentioned here are paired – they will appear on the left and the right side of the neck).

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12. The anterior triangle is situated at the front of the neck bounded by:
Superiorly – Inferior border of the mandible (jawbone)
Laterally – Medial border of the sternocleidomastoid
Medially – Imaginary sagittal line down midline of body.
It can be subdivided into 4 further triangles by the hyoid bone, suprahyoid and infrahyoid muscles.
Subtriangles are named as Carotid, Submental, Submandibular and Muscular

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14. Superior: Posterior belly of the digastric muscle.
Triangle
Carotid triangle
The boundaries:
Superior: Posterior belly of the digastric muscle.
Lateral: Medial border of the sternocleidomastoid muscle.
Inferior: Superior belly of the omohyoid muscle.
The main contents of the carotid triangle are the common carotid artery (which bifurcates within the carotid triangle into the external and internal carotid arteries), the internal jugular vein, and the hypoglossal and vagus nerves.

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16. Triangle
Submental Triangle
Is situated underneath the chin. Its main content is the submental lymph nodes, which filter lymph draining from the floor of the mouth and parts of the tongue.
Is bounded by:
Inferiorly – Hyoid bone.
Medially – Imaginary sagittal midline of the neck.
Laterally – Anterior belly of the digastric.
The base of the submental triangle is formed by the mylohyoid muscle, which runs from the mandible to the hyoid bone.

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18. Submandibular Triangle
Is located underneath the body of the mandible. It contains the submandibular gland (salivary), and lymph nodes. The facial artery and vein also pass through this area.
The boundaries:
Superiorly: Body of the mandible.
Anteriorly: Anterior belly of the digastric muscle.
Posteriorly: Posterior belly of the digastric muscle.

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Muscular Triangle
This anatomical area is situated more inferior than the triangular sub-divisions. It is a slightly dubious triangle, in reality having four boundaries. The muscular triangle is also unique in containing no vessels of note.
It does however contain some muscles and organs – the infrahyoid muscles, the pharynx, and the thyroid, parathyroid glands.
The boundaries are:
Superiorly: The hyoid bone.
Medially: Imaginary midline of the neck.
Supero-laterally: Superior belly of the omohyoid muscle.
Infero-laterally: Inferior portion of the sternocleidomastoid muscle.

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POSTERIOR TRIANGLE
The posterior triangle of the neck (also known as the lateral cervical region), is a region of the neck.
Borders
Anterior: Posterior border of the SCM.
Posterior: Anterior border of the trapezius muscle.
Inferior: Middle 1/3 of the clavicle.
Roof: the investing layer of fascia.
Floor: formed by the prevertebral fascia (see fascial layers of the neck).

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Contents
Muscles: make up the borders and the floor of the area.
A significant muscle in the posterior triangle region in the omohyoid muscle. It is split into two bellies by a tendon. The inferior belly crosses the posterior triangle, travelling in an supero-medial direction, and splitting the triangle into two.
vertebral muscles (covered by prevertebral fascia) form the floor of the posterior triangle:
Splenius captitis 
Levator scapulae
Anterior, Middle and Posterior scalene

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Vasculature
The external jugular vein is one of the major veins of the neck region. Formed by the retromandibular and posterior auricular veins, it lies superficially, entering the posterior triangle after crossing the sternocleidomastoid muscle. Within the posterior triangle, it empties into the subclavian vein.
The transverse cervical and suprascapular veins also lie in the posterior triangle
The subclavian, transverse cervical and suprascapular veins are accompanied by their respective arteries in the posterior triangle.
The distal part of the subclavian artery can be located as it emerges between the anterior and middle scalene muscles. As it crosses the first rib, it becomes the axillary artery, which goes onto supply the upper limb.

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Nerves
The accessory nerve (CN XI) exits the cranial cavity, descends down the neck, innervates sternocleidomastoid and enters the posterior triangle. It crosses the posterior triangle in an oblique, inferoposterior direction, within the investing layer of fascia. It lies relatively superficially in the posterior triangle, leaving it vulnerable to injury.
The cervical plexus forms within the muscles of the floor of the posterior triangle.
Other branches of the cervical plexus innervate the vertebral muscles, and provide cutaneous innervation to parts of the neck and scalp.
The trunks of the brachial plexus also cross the floor of the posterior triangle

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Subdivisions
The omohyoid muscle splits the posterior triangle of the neck into two:
The larger, superior part is termed the occipital triangle. 
The inferior triangle is known as the subclavian triangle and contains the distal portion of the subclavian artery.

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