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In humans, the posterior pharynx is behind the oral opening in the area that's commonly called the top of the throat. The posterior pharynx can be seen at the base of the tongue when the mouth is opened widely. It extends from the uvula, which is the fleshy piece of tissue that hangs at the back of the throat, to the hyoid bone, which sits in the neck between the jawbone, or mandible, and the thyroid cartilage. This area is also referred to as the oropharynx, oral pharynx, or the mesopharynx. The posterior pharynx is part of both the respiratory and digestive systems, and is necessary for vocalization.
The mouth is the start of the digestive system, but it's also part of the respiratory system, as it permits air to pass into the lungs. Within the mouth is the primary organ of taste called the tongue. The back of the tongue, the part located in the very back of the mouth under the uvula, is anchored in the top portion of the posterior pharynx.
The throat called the pharynx, and it's divided into three sections: the nasopharynx at the top, the posterior pharynx in the middle, and the laryngopharynx at the bottom. The nasopharynx sits above the oral pharynx behind the nasal passages. It extends from the bottom of the skull to the soft palate, which is the soft tissue found at the rear portion of the mouth's roof where the uvula is located. The end of the nasopharynx marks the beginning of the posterior pharynx.
The tonsils, known as the palatine tonsils, are located at the side wall of the posterior pharynx. The front wall consists of the epiglottic vallecula, which is a depression between the tongue and the oral pharynx that traps saliva. The superior, or upper, wall consists of the bottom surface of the soft palate and the uvula. The posterior pharynx has a flap of tissue called the epiglottis that covers the glottis to prevent food particles from entering the larynx and traveling into the lungs. The glottis is the part of the larynx that houses the vocal cords.
The lowest portion of the pharynx is the laryngopharynx, which is sometimes called the hypopharynx, and it connects the throat to the esophagus. It sits below the epiglottis and extends to the larynx and the esophagus. This part of the throat diverges into two pathways. The larynx extends into the respiratory tract, and the esophagus extends into the digestive tract.