Under Nysten's law, which muscle group is least likely to stiffen early?

• A. Calf muscles
• B. The muscles of mastication
• C. The muscles of the face
• D. The neck muscles

Answer: (A)

Rigor mortis follows a specific progression described by Nysten's law: it begins in the smaller, more active muscles (like those in the face and neck, and muscles involved in rapid, fine movements such as mastication) and then moves to larger muscle groups, finally involving the largest limb muscles last. Because the calf muscles are large distal muscles, they stiffen later in the sequence, making them the least likely to stiffen early. The other options—face, mastication, and neck muscles—are among the first to stiffen.