Levator submandibuli muscle (Banjo muscle) a rare muscle in human beings; anatomy, morphogenesis, function and incidence

Abstract

A rare muscle named Levator Submandibuli (LS) or Banjo muscle (after the author) is present in few persons. It is situated in the submandibular region superficial to the mylohyoid muscle. It consists of two triangular right and left halves whose fibres originate by interdigitating with each other from a median intermuscular septum attached above to the mandible, below to the hyoid bone, parallel and continuous with the intermuscular septum of the mylohyoid muscle. Levator Submandibuli muscle fibres of each side insert into a tendon which is continuous at each side with the central tendon of the digastric muscles. Contraction of the muscle would elevate and support the submandibular region particularly during swallowing and during any activity which increases the oro-pharyngeal pressure such as blowing a trumpet. The muscle is not an accessory/anomaly of the digastric nor of mylohyoid muscle. Its anatomy indicated that, it is a separate muscle innervated by a branch from the mylohyoid nerve. It is suggested that, there is predilection for the appearance of a separate muscle in the submandiblar region distinct from mylohyoid and digastric muscles. It is further suggested that during myogenesis when the migrating myogenic (myoblasts) cells destined to form levator submandibuli are halted at the proximity of the site of formation of anterior belly of the digastric muscle, an anomalous/accessory muscle of the digastric is formed. But when the myoblasts reach their predestined position in the submandibular region, an independent muscle, levator submandibuli (Banjo muscle) is formed. The muscle has an incidence of about 0.3% in Caucasian and 0.4% in black Africans.