Extensor muscle attachments in hinge joints

Steps:

• Identify the hinge joint, such as the elbow, where extension straightens the angle.
• Locate the extensor muscle, which originates on the proximal bone and inserts on the distal bone.
• Trace attachments: origin near the joint on the upper bone (label 1), insertion on the lower bone away from the joint (label 2).
• Confirm labels 1 and 2 match these points based on diagram positions.

Why A is correct:

• In anatomy, extensors attach to bones on opposite sides of the joint to pull them apart, aligning with origin at 1 and insertion at 2 per standard hinge joint diagrams.

Why the others are wrong:

• B: Labels 3 and 4 likely mark flexor attachments, which bend the joint.
• C: Label 4 is a flexor point; 5 is unrelated, possibly a tendon.
• D: Labels 5 and 6 indicate other structures, not extensor origins or insertions.

Final answer: A