**Core Concept**
Winging of the scapula is a clinical sign characterized by the protrusion of the scapula due to weakness or paralysis of the muscles that stabilize it, particularly the serratus anterior and trapezius muscles. This phenomenon can result from various conditions affecting the nerves that innervate these muscles.

**Why the Correct Answer is Right**
The primary nerve responsible for innervating the serratus anterior muscle is the long thoracic nerve, which originates from the roots of C5-C7. Paralysis of this nerve leads to weakness of the serratus anterior muscle, causing the scapula to protrude and the shoulder to appear "winged." This condition can result from various causes, including nerve injury, tumor, or muscular dystrophy.

**Why Each Wrong Option is Incorrect**
**Option A:** The suprascapular nerve primarily innervates the supraspinatus and infraspinatus muscles, which are involved in shoulder abduction and rotation, but not in scapular stabilization.

**Option B:** The axillary nerve innervates the deltoid and teres minor muscles, which are involved in shoulder flexion, extension, and rotation, but not in scapular stabilization.

**Option C:** The thoracodorsal nerve innervates the latissimus dorsi muscle, which is involved in shoulder extension and adduction, but not in scapular stabilization.

**Clinical Pearl / High-Yield Fact**
A classic mnemonic to remember the nerves responsible for scapular movements is "Serratus: Long Thoracic, Trapezius: Spinal Accessory." This helps to associate the correct nerve with the correct muscle group.

**Correct Answer:** D. Long thoracic nerve.