Bilateral quadrification of the anterior digastric muscles with variations of the median accessory digastric muscles.

During dissection of the submental region, the anterior bellies of the right and left digastric muscles were found to have four separate insertions. Two median accessory digastric muscles were located medially to anterior bellies of the digastrics and inferiorly to the mylohyoid and deep in the platysma. The four accessory muscles of the anterior bellies of the digastric muscles originated from the digastric fossa and inserted into the hyoid bone. Two median accessory digastric muscles were located between the anterior bellies of the digastric muscle and inserted into the hyoid bone as well. These muscle fibers formed a muscular floor for the oral cavity similar to the second mylohyoid muscle. When the muscle heads were analyzed, the anterior belly of the digastric muscle appeared to have six heads. These six heads were united by an intermediate rounded tendon, which was attached to the hyoid bone. This finding of a bilateral quadrification of the anterior digastric muscles with variations in the median accessory digastric muscles has not previously been reported. Anatomic variations of the anterior bellies of the digastric muscles can be easily confused on computed tomographic scans and magnetic resonance imaging. The possible occurrence of such anomalies should be kept in mind during surgical procedures involving the submental region.