**Core Concept:** The external mammary nerve is a branch of the first, second, third, and fourth intercostal nerves, which supply the skin, hair, and nipple of the breast.

**Why the Correct Answer is Right:** The nipple is supplied by the first, second, and third intercostal nerves, which form the external mammary nerve. The fourth intercostal nerve is responsible for the subcutaneous branches that supply the underlying skin.

**Why Each Wrong Option is Incorrect:**
A. The first intercostal nerve (A) is incorrect because it only supplies the skin of the chest wall and does not innervate the nipple.
B. The fourth intercostal nerve (B) is incorrect because it only supplies the subcutaneous tissue of the breast and does not innervate the nipple.
C. The fifth intercostal nerve (C) is incorrect because it is not involved in nipple innervation.
D. The internal mammary nerve (D) is incorrect because it is a branch of the phrenic nerve and supplies the internal mammary glands, not the nipple.

**Clinical Pearl:** The knowledge of the innervation of the nipple is crucial for understanding breast surgery procedures like breast reduction, augmentation, or mastectomy, as preserving the external mammary nerve branches is essential to maintain nipple sensation and erectile function after surgery.

**Correct Answer:** .