Neck anatomy,Fascia,Carotid sheath, Triangles of the neck

ANTERIOR TRIANGLE OF THE NECK
The anterior triangle of the neck is bounded anteriorly by the median
line of the neck and posteriorly by the anterior margin of sternocleidomastoid. Its base is the inferior border of the mandible and its projection to the mastoid process, and its apex is at the manubrium sterni. It
can be subdivided into suprahyoid and infrahyoid areas above and
below the hyoid bone, and into digastric, submental, muscular and
carotid triangles by the passage of digastric and omohyoid across the
anterior triangle (see Fig. 29.5).
Digastric triangle
The digastric triangle is bordered above by the lower border of the
mandible and its projection to the mastoid process, posteroinferiorly
by the posterior belly of digastric and by stylohyoid, and anteroinferiorly by the anterior belly of digastric. It is covered by the skin, superficial
fascia, platysma and deep fascia, which contain branches of the facial
and transverse cutaneous cervical nerves. Its floor is formed by mylohyoid and hyoglossus. The anterior region of the digastric triangle contains the submandibular gland, which has the facial vein superficial to
it and the facial artery deep to it. The submental and mylohyoid arteries
and nerves lie on mylohyoid. The submandibular lymph nodes are
variably related to the submandibular gland. The posterior region
of the digastric triangle contains the lower part of the parotid gland.
The external carotid artery, passing deep to stylohyoid, curves above
the muscle, and overlaps its superficial surface as it ascends deep to the
parotid gland before entering it. The internal carotid artery, internal
jugular vein and vagus nerve lie deeper and are separated from the
external carotid artery by styloglossus,stylopharyngeus and the glossopharyngeal nerve.Submental triangle
The single submental triangle is demarcated by the anterior bellies of
both digastric muscles. Its apex is at the chin, its base is the body of the
hyoid bone and its floor is formed by both mylohyoid muscles. It contains lymph nodes and small veins that unite to form the anterior
jugular vein. The structures within the digastric and submental triangles
are described in more detail with the floor of the mouth.
Muscular triangle
The muscular triangle is bounded anteriorly by the median line of
the neck from the hyoid bone to the sternum, inferoposteriorly by the
anterior margin of sternocleidomastoid and posterosuperiorly by the
superior belly of omohyoid. The triangle contains omohyoid, sternohyoid, sternothyroid and thyrohyoid.
Carotid triangle
The carotid triangle is limited posteriorly by sternocleidomastoid, anteroinferiorly by the superior belly of omohyoid and superiorly by
stylohyoid and the posterior belly of digastric. In the living (except the
obese), the triangle is usually a small visible triangular depression,
sometimes best seen with the head and cervical vertebral column
slightly extended and the head contralaterally rotated. The carotid triangle is covered by the skin, superficial fascia, platysma and deep fascia
containing branches of the facial and cutaneous cervical nerves. The
hyoid bone forms its anterior angle and adjacent floor; it can be located
on simple inspection and verified by palpation. Parts of thyrohyoid,
hyoglossus and inferior and middle pharyngeal constrictor muscles
form its floor. The carotid triangle contains the upper part of the
common carotid artery and its division into external and internal
carotid arteries. Overlapped by the anterior margin of sternocleidomastoid, the external carotid artery is first anteromedial, then anterior to
the internal carotid artery. Branches of the external carotid artery are
encountered in the carotid triangle. Thus the superior thyroid artery
runs anteroinferiorly, the lingual artery anteriorly with a characteristic
upward loop, facial anterosuperiorly,occipital,post.auricular,maxillary.