THYROID AND PARATHYROID GLAND

Muscular Triangle

• Contents:

  • Infrahyoid muscles:

    • Omohyoid

    • Sternohyoid

    • Sternothyroid

    • Thyrohyoid

  • Thyroid gland

  • Parathyroid glands

  • Larynx

  • Trachea

  • Oesophagus

  • Accompanying vessels and nerves of the above viscera

Sternocleidomastoid Muscle

• Origin: Sternal head from manubrium of sternum; Clavicular head from medial one-third of clavicle

• Insertion: Lateral surface of mastoid process

• Innervation: Accessory nerve [XI], branches from anterior rami of C2 to C3

• Function:

  • Individually, tilts head toward shoulder on same side

  • Together, draw head forward or rotate head

Bones of the Anterior Triangle of the Neck

• Structures:

  • Greater and lesser horns of hyoid bone

  • Body of hyoid bone

  • Anterior border, ramus, and mental foramen

Suprahyoid Muscles

• Contents:

  • Found in the submental and submandibular triangles

  • Muscles:

    • Stylohyoid

      • Origin: Base of styloid process

      • Insertion: Lateral area of body of hyoid bone

      • Innervation: Facial nerve [VII]

      • Function: Pulls hyoid bone upward in posterior-superior direction

    • Digastric (anterior and posterior belly)

      • Functions to open mouth by lowering mandible

    • Mylohyoid

      • Supports and elevates floor of mouth

    • Geniohyoid

      • Pulls hyoid bone forward; elevates mandible

Infrahyoid Muscles

• Contents:

  • Found in muscular and carotid triangles

  • Muscles:

    • Sternohyoid

      • Origin: Posterior aspect of manubrium of sternum

      • Function: Depresses hyoid bone after swallowing

    • Omohyoid

      • Function: Depresses and fixes hyoid bone

    • Thyrohyoid

      • Function: Depresses hyoid bone; raises larynx when hyoid is fixed

    • Sternothyroid

      • Function: Draws larynx downward

Thyroid Gland

• Location: Anterior neck, below and lateral to thyroid cartilage

• Structure:

  • Large unpaired gland with two lateral lobes connected by an isthmus

  • Lies deep to sternohyoid, sternothyroid, and omohyoid muscles

• Development:

  • Arises from pharyngeal outgrowths; originates from foramen cecum via thyroglossal duct

• Arterial Supply:

  • Superior thyroid artery (from external carotid)

  • Inferior thyroid artery (from thyrocervical trunk)

  • Thyroid ima artery (occasionally)

• Venous and lymphatic drainage:

  • Superior, middle, and inferior thyroid veins; lymph nodes (paratracheal and deep cervical)

Parathyroid Glands

• Description:

  • Two pairs of small, yellowish structures on deep surface of lateral lobes of thyroid gland

• Origin:

  • Derived from 3rd (inferior glands) and 4th (superior glands) pharyngeal pouches

• Blood Supply: Inferior thyroid arteries

• Drainage: Shares venous and lymphatic pathways with thyroid gland