**Core Concept**
The spleen is an organ that filters the blood and stores red blood cells. Splenules or splenuli are accessory spleens, which are small nodules of splenic tissue that can be found at various locations in the abdominal cavity. The presence of accessory spleens is a common phenomenon, and identifying their most common location is crucial for surgeons and radiologists.

**Why the Correct Answer is Right**
The splenic hilum is the region where the splenic artery, vein, and nerves enter and exit the spleen. Accessory spleens are often found in close proximity to the main spleen and can be located in the splenic hilum. This is because the splenic tissue in the hilum is a remnant of the embryonic development of the spleen. The splenic hilum is a common location for accessory spleens because it contains a high concentration of splenic tissue and is a site of frequent surgical exploration.

**Why Each Wrong Option is Incorrect**
**Option A:** Behind the tail of pancreas is not a common location for splenules. While the pancreas and spleen are adjacent organs, the tail of the pancreas is not a typical site for accessory spleens.

**Option B:** Splenic ligaments are structures that connect the spleen to adjacent organs, but they are not a common location for splenules. The ligaments are primarily composed of connective tissue and do not contain significant amounts of splenic tissue.

**Option D:** Mesocolon is a fold of peritoneum that attaches the colon to the abdominal wall. While accessory spleens can be found in the mesocolon, it is not the most common location.

**Clinical Pearl / High-Yield Fact**
When performing splenectomy or exploring the abdominal cavity, it is essential to identify and remove all accessory spleens to prevent recurrence of splenic function and potential complications.

**✓ Correct Answer: C. Splenic hilum**