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.