**Core Concept**
The femoral ring is an anatomical structure located in the anterior abdominal wall, which serves as a passageway for the femoral vessels. It is bounded by several structures that play a crucial role in its formation. The medial boundary of the femoral ring is formed by a specific ligament that plays a significant role in the region's anatomy.

**Why the Correct Answer is Right**
The lacunar ligament, also known as Gimbernat's ligament, is a fibrous structure that forms the medial boundary of the femoral ring. It is a part of the inguinal ligament, which is a fibrous band that runs from the pubic tubercle to the anterior superior iliac spine. The lacunar ligament is a semilunar fibrocartilaginous structure that is located just medial to the femoral vein. It is a critical landmark in the region and is often used as a reference point in surgical procedures.

**Why Each Wrong Option is Incorrect**
**Option A:** The inguinal ligament is a broad, flat band that forms the floor of the femoral canal, but it does not form the medial boundary of the femoral ring.

**Option B:** The pecten pubis is a small, triangular bone that is located on the pubic bone, but it is not directly involved in the formation of the femoral ring.

**Option D:** The conjoint tendon is a fibrous structure that is formed by the fusion of the aponeuroses of the internal oblique and transversus abdominis muscles. It is located lateral to the femoral ring and does not form its medial boundary.

**Clinical Pearl / High-Yield Fact**
The lacunar ligament is an important landmark in the region, and knowledge of its anatomy is crucial for surgeons and clinicians performing procedures in the femoral region. It is also a useful reference point for identifying other structures in the region, such as the femoral vein and the femoral canal.

✓ Correct Answer: C. Lacunar ligament