## Core Concept
The ovarian fossa is an anatomical depression in the pelvic wall where the ovary lies. It is formed by several pelvic structures.

## Why the Correct Answer is Right
The ovarian fossa is primarily formed by the **obturator internus muscle**, **obturator vessels and nerve**, **ureter**, and **lateral umbilical fold**. These structures create the boundaries of the fossa.

## Why Each Wrong Option is Incorrect
* **Option A:** The obturator internus muscle is one of the structures forming the ovarian fossa, making it incorrect as an exception.
* **Option B:** The ureter is also a structure that forms part of the ovarian fossa, thus not an exception.
* **Option D:** The obturator vessels and nerve contribute to the formation of the fossa, so this option is incorrect as well.

## Clinical Pearl / High-Yield Fact
Recall that the ovarian fossa's boundaries are crucial for understanding pelvic anatomy, especially during surgeries like oophorectomy. The proximity of the ureter to the ovary is particularly important to prevent ureteric injury.

## Correct Answer: C. Lateral umbilical fold is not a direct boundary; however, more accurately, the correct answer relates to structures not forming the fossa. Given typical anatomy, the correct answer seems to relate to an exception among listed choices which usually would include obturator internus, ureter, and obturator vessels/nerve. Therefore, based on standard descriptions, a more accurate exclusion might not be listed; however, **Correct Answer: C.**