Culmen

the Shibboleth and Culmen of Honesty

Source: wiktionary

The measurements were taken as follows: wing length, from the carpal joint to the tip of the longest primary; tarsus length, from the tibiotarsal joint to the distal undivided scute; upper mandible length, the chord length from the point where the culmen enters the feathers of the head to the tip; bill depth, in the vertical plane level at the anterior edge of the nares.

Source: wiktionary

A very simple form was found in the carving shown in Pl. 17, fig. 13, where a long projecting knob is seen at the base of the culmen.

Source: wiktionary