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The triangles of the neck
This specimen shows the anterior and the posterior triangles in the side of the neck.
The side of the neck is divided into the anterior triangle and the posterior triangle by the sternocleidomastoid muscle.
The anterior triangle is further subdivided into three and a half triangles, namely, the submental triangle, the digastric triangle, the carotid triangle and the muscular triangle, by the digastric muscle and the omohyoid muscle (superior belly). The important structures of anterior triangle are the common carotid artery, the external carotid artery, the internal carotid artery, the internal jugular vein, the ansa cervicalis, the accessory nerve, the vagus nerve, the hypoglossal nerve, the submandibular salivary gland, the facial artery Structures such as and the External carotid artery can be identified in the anterior triangle.
The posterior triangle is further subdivided into the occipital triangle and subclavian triangle by the omohyoid muscle (inferior belly). The important structures of the posterior triangle are the spinal accessory nerve, the subclavian artery (3rd part), the trunks of the brachial plexus, the terminal part of the External jugular vein along with the four cutaneous nerve, namely, the lesser occipital nerve, the great auricular nerve, the transverse cervical nerve, the supraclavicular nerve.
Sternocleidomastoid:
The sternocleidomastoid is present in the side of the neck. Its origin lies at the manubrium sterni and the medial one third of the clavicle and its insertion lies at the mastoid process. It is supplied by the spinal accessory nerve. When one muscle contracts, it turns the chin to the opposite side and when both muscles contract, it pulls the head forwards. Its spasm leads to torticollis or wry neck. In this condition, the head is bent to one side and the chin points to the opposite side.
Digastric muscle:
The digastric muscle presents two bellies, namely, the anterior belly and the posterior belly. The anterior belly takes origin from the chin and the posterior belly from the mastoid process. Both these bellies insert into the intermediate tendon which is attached to the hyoid bone by the deep cervical fascia. The anterior belly is supplied by the mandibular nerve and the posterior belly is supplied by the facial nerve. Both bellies elevate the hyoid bone.
Omohyoid muscle:
The omohyoid muscle presents two bellies, namely, the inferior belly and the superior belly. The inferior belly takes origin from the scapula (superior border near the suprascapular notch) and the superior belly takes origin from the hyoid bone. Both these bellies insert into the intermediate tendon which is attached to the clavicle by the deep cervical fascia. Both the bellies are supplied by the ansa cervicalis. Both bellies depress the hyoid bone.
Hypoglossal nerve:
The hypoglossal nerve is the twelfth cranial nerve. It supplies the muscles of the tongue. The nerve passes through the hypoglossal canal at the base of the skull, lies deep to the parotid gland, then lies in the carotid triangle and the digastric triangle of the neck. Further, it passes through the submandibular region, lies superficial to the hyoglossus muscle and then supply the muscles of the tongue.
Submandibular salivary gland:
The submandibular salivary gland is a mixed salivary gland. It lies in the digastric triangle. It has a large superficial part and a smaller deep part. The submandibular duct arises from the deep part. It opens into the sublingual papilla in the floor of the mouth.
Facial artery:
The facial artery is a branch of the external carotid artery given off in the carotid triangle. It comes to lie close to the submandibular salivary gland, enters the face and then supplies the face. The face is highly vascular. Therefore, wounds and surgeries on the face heal rapidly.
External carotid artery:
The external carotid artery is the terminal branch of the common carotid artery given off in the carotid triangle at the upper border of the thyroid cartilage. It gives eight branches that supply various structures in the neck, face and the scalp.
Lesser occipital nerve:
The lesser occipital nerve is a cutaneous nerve arising from the cervical plexus. Its root value is C2. It supplies the skin of the scalp posterior to the auricle.
Great auricular nerve:
The great auricular nerve is a cutaneous nerve arising from the cervical plexus. Its root value is C2, C3. It supplies the skin of the scalp posterior to the auricle and the skin over the parotid gland.
Transverse cervical nerve:
The transverse cervical nerve is a cutaneous nerve arising from the cervical plexus. Its root value is C2, C3. It supplies the skin of the front of the neck.
Supraclavicular nerve:
The supraclavicular nerve is a cutaneous nerve arising from the cervical plexus. Its root value is C3, C4. It supplies the skin of the upper part of the chest and the skin over the deltoid muscle.
Spinal accessory nerve:
The accessory nerve is the eleventh cranial nerve. It consists of two parts, namely, the cranial part and the spinal part. The spinal accessory nerve supplies the sternocleidomastoid and the trapezius. Its damage leads to paralysis of the muscles supplied by it.
External jugular vein:
The external jugular vein is formed at the apex of the parotid gland by the posterior division of retromandibular vein and the posterior auricular vein. It descends superficial to the sternocleidomastoid and then pierces the deep cervical fascia in the posterior triangle to drain into the subclavian vein. If the external jugular vein is cut at the point where it pierces the deep cervical fascia, its walls cannot collapse. This causes air to get sucked into it during inspiration leading to a clinical condition known as venous air embolism, subsequently leading to death. The external jugular vein is used to assess the venous pressure in the right atrium.
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