**Core Concept**
The transverse mesocolon is a fold of peritoneum that attaches the transverse colon to the posterior abdominal wall, creating a potential space between the colon and the abdominal wall. This space contains various structures, including blood vessels.

**Why the Correct Answer is Right**
The transverse mesocolon contains the middle colic artery and vein, which are branches of the superior mesenteric artery and vein. These vessels supply the transverse colon with oxygenated blood and are responsible for its innervation. The middle colic vessels run within the transverse mesocolon and are crucial for the blood supply of the transverse colon.

**Why Each Wrong Option is Incorrect**
**Option A:** The left colic artery and vein are not contained within the transverse mesocolon; they are branches of the inferior mesenteric artery and vein and supply the descending colon.
**Option B:** The right colic artery and vein are contained within the ascending mesocolon, not the transverse mesocolon; they supply the ascending colon.
**Option C:** The ileocolic artery and vein are contained within the mesentery of the small intestine, not the transverse mesocolon; they supply the terminal ileum and the cecum.

**Clinical Pearl / High-Yield Fact**
The transverse mesocolon is a common site for bleeding during laparoscopic cholecystectomy or other abdominal surgeries, particularly when the middle colic vessels are injured. Recognizing the anatomy of the transverse mesocolon is essential for surgeons and radiologists to avoid complications.

**Correct Answer:** C. Middle colic artery and vein.