The neck contains four layers of deep fascia that divide it into compartments. The sides of the neck are divided into anterior and posterior triangles by the sternocleidomastoid muscle. The anterior triangle contains the submandibular gland and carotid arteries, while the posterior triangle contains nerves of the brachial plexus and subclavian vessels. Major structures in the neck include the pharynx, which is divided into nasopharynx, oropharynx, and laryngopharynx, and the larynx, which is a cartilaginous structure that acts as an air valve and aids in voice production. The thyroid gland lies in the neck anterior to the trachea.

1. Layers of the Neck
1) Skin: is supplied by cervical spinal nerves
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2) Superficial fascia; it contains Platysma muscle and superficial veins
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3) Deep fascia; is tight, dividing the neck into different compartments as it has 4 layers.
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A) Investing layer: it surrounds the whole neck like a collar
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B) Pre-tracheal layer; Around the thyroid gland.
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C) Pre-vertebral layer; Around pre vertebral muscles.
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D) Carotid sheath; Around common carotid arteries, internal jugular vein and vagus nerve.
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Triangles of the Neck
The side of the neck is subdivided into anterior and posterior triangles by the sternomastoid muscle which
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crosses the neck obliquely.
1) Anterior triangles;
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Boundaries;
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A) Posteriorly; anterior border of sternomastoid muscle
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B) Anteriorly; middle line of the neck
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C) Superiorly; lower border of the mandible
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1.1) Digastric triangle; it contains the submandibular salivary gland and facial vessels.
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1.2) Carotid triangle; it contain carotid arteries UV, vagus nerve, and hypoglossal nerve.
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1.3) Muscular triangle; it contains the infrahyoid muscles.
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1.4) Submental triangle; it is half a triangle in each side.
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2) Posterior triangle;
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Boundaries;
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A) Anteriorly; Sternomastoid muscle
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B) Posteriorly; Trapezius muscle
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C) Inferiorly; Middle third of the clavicle
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Contents;
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A) Spinal part of accessory nerve
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B) Subclavian vessels
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C) Brachial plexus
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Viscera of the Neck
The Pharynx;
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A muscular tube extends from skull base to C6 vertebra (it continues as the esophagus.)
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It lies anterior to the cervical vertebrae but posterior to nasal cavity mouth cavity and larynx. It has no anterior
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wall.
It acts as digestive and respiratory passage.
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Parts; it is divided into 3 parts
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1) Nasopharynx; lies behind nasal cavity.
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It contains;
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A) Adenoids (Pharyngeal tonsils); lymphatic collections below the mucosa of its posterior wall.
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B) Pharyngeal end of the Eustachian tubes which connects nasopharynx to the middle ear.
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2) Oropharynx; lies behind the mouth cavity. It contains palatine tonsils and lingual tonsils.
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3) Laryngopharynx; lies behind the larynx.
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The larynx;
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A cartilaginous box present in the neck and performs many functions.
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1) Acts as an open valve in respiration
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2) Has a role in voice production.
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3) it is closed during devolution to prevent passage of solids to lower respiratory parts.
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Site; in the neck in front of C4-C6 vertebrae and pharynx.
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2. Structure; it is composed of cartilages , connected together by membranes and muscles.
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Single cartilages;
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A) Thyroid; formed of plates connected Anteriorly giving.
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B) Cricoid; is ring like and continue below larynx as the trachea.
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C) Epiglottis; closes the laryngeal inlet during deglutition.
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Paired cartilages; as arytenoids.
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Cavity of the larynx; it contains 2 folds on the each side upper vestibular and lower vocal.
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It can divided into;
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1) laryngeal inlet
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2) vestibule; between inlet and vestibular fold.
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3) Sinus; between vestibular and vocal folds.
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4) infra glottic area; below vocal cords
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The thyroid gland;
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An endocrine gland that lies in the neck
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It has 2 pyramidal lobes connected by an isthmus.
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Each lobe extends between oblique line of thyroid cartilage and 4th or 5th tracheal ring.
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Isthmus lies opposite 2nd - 4th tracheal rings.
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Parathyroid glands are 2 pairs (superior and inferior) located on posterior border of thyroid gland.
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