**Core Concept**
The ligament of Poupart, also known as the inguinal ligament, is a fibrous band that runs from the anterior superior iliac spine to the pubic tubercle in the inguinal region. It forms the floor of the inguinal canal and separates the deep inguinal ring from the superficial inguinal ring.

**Why the Correct Answer is Right**
The inguinal ligament plays a crucial role in the anatomy of the inguinal region, serving as a significant landmark for various surgical procedures and clinical examinations. It is formed by the fusion of the aponeuroses of the external oblique muscle and is reinforced by the pectineal ligament, which is a fibrous band that connects the pubic bone to the pectineal line of the pubic bone. The inguinal ligament is also an important structure in the prevention of inguinal hernias, as it helps to maintain the integrity of the inguinal canal.

**Why Each Wrong Option is Incorrect**
**Option A:** The linea alba is a fibrous structure that runs along the midline of the abdomen from the xiphoid process to the pubic symphysis, but it is not the ligament of Poupart.
**Option B:** The pectineal ligament is a fibrous band that connects the pubic bone to the pectineal line of the pubic bone, but it is not the ligament of Poupart.
**Option C:** The lacunar ligament, also known as the Gimbernat's ligament, is a fibrous structure that forms the medial boundary of the femoral triangle, but it is not the ligament of Poupart.

**Clinical Pearl / High-Yield Fact**
The ligament of Poupart is a significant landmark for the identification of the femoral artery and vein, which can be palpated below the inguinal ligament in the femoral triangle.

**✓ Correct Answer: D. Inguinal ligament**