Larynx

The larynx is an inferior continuation of the oropharynx. It extends from the epiglottis (namely the glossoepiglottic and pharyngoepiglottic folds) to the inferior aspect of the cricoid cartilage. Inferiorly, it continues as the cervical trachea. 

Gross anatomy

The larynx consists of a cartilage "skeleton", as well as internal structures that are divided into three subsites, mainly for the purposes of laryngeal cancer staging:

• supraglottis: extends from the tip of the epiglottis to the laryngeal ventricle
  • epiglottis: divided into suprahyoid and infrahyoid portions
  • pre-epiglottic space
  • arytenoid cartilages
  • aryepiglottic folds
  • false vocal cords
  • paraepiglottic space
• glottis
  • true vocal cords
  • anterior commissure
  • posterior commissure
• subglottis: extends from the inferior surface of the true vocal cords to the inferior aspect of the cricoid cartilage

Relations

• anterior: strap muscles, anterior jugular vein
• posterior: esophagus, laryngopharynx
• superior: hyoid bone, laryngopharynx
• inferior: trachea

Arterial supply

• above the vocal cords: superior laryngeal artery (branch of the superior thyroid artery)
• below the vocal cords: inferior laryngeal artery (branch of the inferior thyroid artery)

Venous drainage

• above the vocal cords: superior laryngeal vein accompanies its artery and drains into the superior thyroid vein (a tributary to the internal jugular vein)
• below the vocal cords: inferior laryngeal vein accompanies its artery and drains into the inferior thyroid vein (a direct tributary to the brachiocephalic vein)

Lymphatic drainage

• supraglottic: the supraglottic lymphatic network follows the superior laryngeal artery, piercing the thyrohyoid membrane and then draining into the superior deep cervical nodes and the pre-epiglottic nodes ⁶. 
• subglottic: the infraglotttic lymphatic network drains to the inferior deep cervical nodes, following the inferior laryngeal artery, and/or the prelaryngeal (Delphian) nodes via the conus elasticus (aka the lateral cricothyroid ligaments) ⁶. 

Both the superior and inferior deep cervical nodes then drain into the right and left jugular trunks, which subsequently empty into the right lymphatic duct and the thoracic duct on the left. 

Innervation

• motor: the recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx apart from the cricothyroid muscle, which is supplied by the external laryngeal nerve
• sensory: 
  • above the vocal cords (supraglottic): internal laryngeal nerve (branch of the superior laryngeal nerve)
  • below the vocal cords (infraglottic): recurrent laryngeal nerve

Development

• the larynx is formed from the laryngotracheal groove, which is related to the caudal aspect of the floor of the primordial pharynx
• the cartilages of the larynx develop from the 4^th and 6^th pharyngeal arches