The layer generally present only in thick, coarse hair is which of the following?

• A. Cuticle
• B. Medulla
• C. Cortex
• D. Hair shaft

Answer: (B)

The medulla is the inner core of the hair shaft and is the layer most commonly present in thick, coarse hair. Its presence tends to increase with hair diameter, so coarse hair often has a continuous medulla, while finer hair may have little to no medulla or a fragmented one. The other structures—cuticle as the outer protective layer and cortex as the main middle layer that provides mass and pigment—are present in hair of all thicknesses, and the term hair shaft refers to the entire structure, not a single layer. So the medulla fits the description of a layer generally present only in thick, coarse hair.