Connects SDF muscle to distal radius

• A. SDF check ligament
• B. DDF check ligament
• C. Lacertus fibrosus
• D. Collateral ligaments

Answer: (A)

The main idea is how the stay apparatus uses check ligaments to anchor flexor tendons to bone, so the limb can bear weight with less muscular effort. The superficial digital flexor (SDF) muscle connects to the distal radius through its check ligament. This ligament ties the SDF tendon to the radius, limiting proximal movement of the tendon during weight bearing while still allowing the tendon to transmit force to flex the digit when needed. The other options involve different structures: the deep digital flexor has its own check ligament to the radius, not the SDF; the lacertus fibrosus links the biceps brachii tendon to other forelimb tissues rather than directly connecting the SDF to the distal radius; and collateral ligaments are joint stabilizers, not connections between the SDF tendon and the radius.