What describes a fusiform muscle?

• A. Thick in the center and tapered at the ends
• B. Four-sided muscle
• C. Formed by parallel fibers
• D. Sphincters that close off tubes

Answer: (A)

Fusiform muscles are spindle-shaped, with a broad, rounded belly in the middle and tapered ends where the tendons attach. This design allows a muscle to shorten efficiently along its length, producing rapid contraction. The fibers run largely parallel to the long axis, contributing to that quick shortening.

The description that matches this shape is a thick center with tapered ends. The other options describe different muscle forms—four-sided refers to a rectangular shape, and sphincters are circular muscles that close passages. While parallel fibers can be present, the defining feature is the central belly that tapers at the ends.