Finger Joints That Stick Out When They Are Bent

This page is the CodyCross answer for the clue below from Architectural Styles, Group 1168, Puzzle 2 (Domed Ceilings).

Question is: Finger Joints That Stick Out When They Are Bent

and the answer is: KNUCKLES

Word Meaning:

KNUCKLES — plural of knuckle

Definitions from Wiktionary.