The dorsal ridge of a bird's bill.

the upper edge or ridge of upper mandible.

A standard measure used by bird banders; it is the straight-line measure of the top edge of the upper bill from its tip to the point where feathers begin to cover its base.

The culmen is the uppermost central ridge of the upper mandible. There is no specific function associated with it, but males tend to have a larger culmen than females.

upper ridge of maxilla

Upper ridge on bill.

The lengthwise ridge running down the middle of the uppper mandible or beak/bill.