ABSTRACT
Superior constrictor (11) arises from the medial pterygoid plate and the pterygomandibular raphe, which ensures continuity between it and buccinator. Middle constrictor (12) arises from the hyoid bone and stylohyoid ligament. Inferior constrictor arises from the thyroid and cricoid cartilages: thyropharyngeus (13) and cricopharyngeus (14). The constrictors sweep around the pharynx and fuse in the pharyngeal raphe (15). They overlap each other and the pharyngobasilar fascia so that much of the pharynx has three layers in its wall. More inferiorly, there may be only middle and inferior constrictors, leaving a possible weakness in the wall and the potential for the formation of a pharyngeal diverticulum (pouch). Cricopharyngeus forms a sphincteric ring around the lower pharynx and is only open during swallowing. Otherwise air would be sucked into the oesophagus during thoracic expansion for inhalation.
