3.4 Describe the boundaries of the triangles of the neck and their respective contents.

Muscular Triangles of the Neck The sternocleidomastoid muscle divides the neck into the anterior and posterior triangles.

A. Anterior Triangle of the NeckBoundaries:Anterior: Midline of the neckPosterior: Anterior border of the sternocleidomastoid muscleSuperior: Lower border of the mandibleRoof: Skin, superficial fascia, platysma

Subdivisions: subdivided by two muscles1. Digastric muscle2. Superior belly of the omohyoid

Into 4 triangles1. Submandibular triangle (Digastric)2. Carotid triangle3. Submental triangle4. Muscular triangle

I. Submandibular triangle or Digastric Triangle Below the body of the mandibleBoundaries:Anteroinferior: Anterior belly of the digastric musclePosteroinferior: Posterior belly of the digastric muscle + stylohyoid muscleSuperior: Lower border of the mandibleFloor: Mylohoid and hyoglossus musclesRoof: investing layer of deep cervical fasciaContents:Facial ArteryHypoglossal Nerve (XII)Submandibular salivary gland

II. Carotid Triangle or Superior Carotid Triangle Behind the Hyoid MuscleBoundaries:Inferomedial: Superior belly of the omohyoid muscleInferolateral: Anterior border of the sternocleidomastoid muscleSuperior: Posterior belly of the digastric muscleFloor:Middle pharyngeal constrictor muscleInferior pharyngeal constrictor muscleThyrohyoid muscleContents:Carotid SheathExternal Jugular Vein

III. Submental Triangle or Suprahyoid Triangle Below the chinBoundaries:Right and Left: Anterior bellies of the right and left digastric musclesInferior: Body of the hyoid boneFloor: Mylohyoid muscleRoof: Investing layer of the deep cervical fasciaContents: Submental Lymph nodes

IV. Muscular Triangle or Inferior Carotid Triangle Below the Hyoid boneBoundaries:Medial: Median plane of the neckSuperolateral: Superior belly of the omohyoid muscleInferolateral: Anterior Border of the sternocleidomastoid muscleContents:Anterior Jugular VeinInfrahyoid musclesBeneath the floor: thyroid gland, larynx, trachea, esophagus

B. Posterior Triangle of the NeckBoundaries:Anterior: Posterior border of the sternocleidomastoidPosterior: Anterior border of the trapezius muscleInferior: Middle 1/3 of the clavicleRoof: investing layer of the deep cervical fasciaFloor: muscles of the neck covered by pervertebral fascia

Subdivisions: subdivided by the inferior belly of the omohyoid muscle1. Occipital triangle (above)2. Supraclavicular triangle (below)

I. Occipital Triangle Larger division of the posterior triangleBoundaries:Anterior: Sternocleidomastoid musclePosterior: TrapeziusInferior: Inferior belly of the omohyoid muscle

II. Supraclavicular Triangle Also called subclavian triangle Smaller division of the posterior triangle Formed by the first rib with the first digitations of the serratus anteriorBoundaries:Inferior: ClavicleSuperior: Inferior belly of the omohyoid muscleBase: Posterior border of the sternocleidomastoid muscle