In vertical wall cracks of a claw, the crack begins in which tissue?

• A. Intercellular cement
• B. Keratin
• C. Dermal layer
• D. Sebum

Answer: (A)

Vertical wall cracks in a keratinized claw start where the cells that make up the wall connect to each other. The nail or claw wall is built from keratinized cells that are glued together by intercellular cement—an adhesive-rich layer that fills the spaces between cells. When this cement breaks down or dries out, the cells separate at their boundaries, and a crack propagates along those intercellular gaps. Keratin provides the sturdy framework, but the initial failure occurs at the cell-to-cell junctions where the cement holds the cells together. The deeper dermal layer isn’t the source of cracks in the hard surface, and sebum is just a lubricant secretion, not a tissue that forms the crack.