Middle pharyngeal constrictor

The middle pharyngeal constrictor is the second of the three circular muscles of the pharyngeal wall, lying between the superior and inferior constrictors.

Origin

The middle pharyngeal constrictor is fan-shaped with fibres diverging posteriorly and superiorly/inferiorly from their origin. It has two main parts based on its origin from the hyoid bone and stylohyoid ligament:

• Ceratopharyngeal part: From the greater horn (cornu) of the hyoid bone.

• Chondropharyngeal part: From the lesser horn (cornu) of the hyoid bone and the stylohyoid ligament.

Insertion

Fibres sweep posteriorly and medially to insert into the median pharyngeal raphe, where they interlace with fibres from the opposite side. The upper fibres overlap the superior pharyngeal constrictor, while the lower fibres are overlapped by the inferior pharyngeal constrictor.

Innervation

Receives motor supply from the pharyngeal branch of the vagus nerve (cranial nerve X) via the pharyngeal plexus, containing motor fibres from the cranial part of the accessory nerve (CN XI).

Relations

• Superiorly: Overlapped by the superior constrictor. The glossopharyngeal nerve (CN IX) and stylopharyngeus muscle pass through the interval between the two muscles.

• Inferiorly: Overlapped by the inferior constrictor near the thyroid cartilage.

Action

The middle pharyngeal constrictor muscle constricts the middle portion of the pharynx during swallowing, propelling the food bolus downward from the oropharynx to the laryngopharynx. It acts sequentially after the superior constrictor and before the inferior constrictor, contributing to the peristaltic wave of pharyngeal contraction.