The<unk>  (or Meckel's<unk> ,<unk>  fossa, or<unk>  foramen, or<unk>  canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the<unk>  cartilage. Modern eutherian mammals (which includes placental mammals) do not have a<unk> .
Meckelian groove
Kronig isthmus
Umbilical-urachal sinus
Nicomachus 
Sternal cleft
Phrygian cap 
Clitoral hood
Muscular triangle