Which muscle is bipennate?

• A. Dorsal Interosseous Muscle
• B. Plantar Interosseous Muscle
• C. Flexor Digitorum Longus
• D. Tibialis Posterior

Answer: (B)

Bipennate describes a muscle whose fibers attach on both sides of a central tendon, giving a feather-like appearance and allowing a larger amount of muscle fibers to share a single tendon. The plantar interosseous muscles fit this arrangement in the foot: they originate from the medial sides of the 3rd–5th metatarsals and insert on the medial sides of the proximal phalanges of the same toes, with their fibers radiating around a central tendon toward the toes. This setup creates a two-sided (bipennate) fiber pattern that enables strong, compact force generation to adduct the toes toward the second toe and stabilize the metatarsophalangeal joints. The other muscles listed have different fiber patterns and primary actions that don’t match the bipennate description in this context.