In a study of 390 mylohyoid grooves in dry mandibles and in dissections of the region, the groove conformed to the classic description (that is, it was open along its entire length) in only 83.6% of the cases. In the remaining 16.4%, the sulcus was partially or totally converted to a bony canal by ossification of the membrane that covered it. When only partially converted, the ossification was proximal or distal, single or multiple. This ossification is explained according to the embryological origin of the membrane closing the canal from Meckel's cartilage. The practical importance of these observations in anatomical dissection and in surgical intervention in the region is discussed.