## Core Concept
The inguinal canal is a significant passage through the lower abdominal wall, allowing for the spermatic cord in males and the round ligament of the uterus in females to pass through. It is bounded by several structures, and understanding its anatomy is crucial for surgical and clinical purposes. The posterior wall of the inguinal canal is particularly important for preventing hernias.

## Why the Correct Answer is Right
The posterior wall of the inguinal canal is primarily formed by the **transversalis fascia**, which is a layer of connective tissue. Additionally, the **internal oblique muscle** and the **transversus abdominis muscle** contribute to its formation, especially in the lateral part. However, the key structure that is often considered as not forming the posterior wall is the **external oblique muscle**. The external oblique muscle forms the anterior wall of the inguinal canal, not the posterior wall.

## Why Each Wrong Option is Incorrect
- **Option A:** The transversalis fascia is indeed a part of the posterior wall, making it an incorrect choice as the structure not bounding the posterior wall.
- **Option B:** If a structure like the internal oblique muscle or part of it contributes to the posterior wall, then it would not be the correct answer to the question of which does NOT bound the posterior wall.
- **Option C:** Similarly, if another structure like the conjoint tendon (formed by the internal oblique and transversus abdominis muscles) is part of the posterior wall, it would not be the correct answer.

## Clinical Pearl / High-Yield Fact
A significant clinical correlation is the **Hesselbach's triangle**, which is a region in the anterior abdominal wall defined by the lateral border of the rectus sheath medially, the inferior epigastric artery laterally, and the inguinal ligament inferiorly. Weakness in this area can lead to direct inguinal hernias, which occur through the posterior wall of the inguinal canal.

**Correct Answer: D. External oblique muscle.**