Identifying the ulna in rabbit forelimb anatomy

Steps:

• Recall that the rabbit forelimb includes humerus (upper arm), radius and ulna (forearm), and distal bones like carpals.
• Note the ulna as the longer, medial forearm bone articulating with the humerus and carpus.
• Examine diagram labels: A points to the slender bone parallel to the radius but more posterior/medial.
• Match label A to ulna's position relative to humerus and radius.

Why A is correct:

• The ulna is defined as the bone on the medial side of the forearm, forming the elbow joint with the humerus, which matches label A's location.

Why the others are wrong:

• B labels the radius, the lateral forearm bone that rotates for pronation/supination.
• C labels the humerus, the single upper arm bone proximal to the forearm.
• D labels a carpal bone, part of the wrist distal to the ulna.

Final answer: A