Crest (4)
'crest' is the definition.
(geographical term)
This is all the clue.
(Other definitions for ridge that I've seen before include "Line where two upward sloping surfaces meet" , "watershed ..." , "there's a lot of pressure in it" , "German Baltic port, Buxtehude home" , "Top of sloping roof" .)
(Other definitions for apex that I've seen before include "reasonable fare" , "The highest point or peak" , "crown" , "The highest point or pointed end" , "climax" .)
'crest' is the definition.
(I know that comb is a type of crest)
This is all the clue.
(Other definitions for comb that I've seen before include "Tidy (hair); some honey" , "Implement with teeth" , "Fowl's crest" , "Carefully search" , "Search methodically" .)