**Core Concept**
The question is testing the student's knowledge of the motor innervation of the hand, specifically the nerves responsible for thumb and finger opposition. The ulnar nerve and median nerve are the two primary nerves involved in hand function, with the ulnar nerve controlling the adductor pollicis muscle and the median nerve controlling the thenar muscles.

**Why the Correct Answer is Right**
Opposition of the thumb and little finger is a complex movement that requires the coordinated action of multiple muscles. The ulnar nerve innervates the adductor pollicis muscle, which adducts the thumb, while the median nerve innervates the thenar muscles, which oppose the thumb. The inability to oppose the tips of the little finger and the thumb suggests a lesion of the ulnar nerve, which is responsible for the motor innervation of the adductor pollicis muscle.

**Why Each Wrong Option is Incorrect**
* **Option A:** The radial nerve is primarily responsible for wrist extension and finger extension, and is not involved in thumb and finger opposition.
* **Option B:** The musculocutaneous nerve innervates the biceps and brachialis muscles, which are involved in elbow flexion, and is not involved in hand function.
* **Option C:** The axillary nerve is primarily responsible for shoulder function, and is not involved in hand function.

**Clinical Pearl / High-Yield Fact**
The ulnar nerve is often injured at the elbow, where it is susceptible to compression due to the proximity of the medial epicondyle. This can result in a classic clinical presentation known as "claw hand," characterized by the inability to oppose the thumb and fingers.

**Correct Answer:** C. The ulnar nerve.