**Core Concept:** The inguinal canal is a passage in the abdominal wall that contains the internal inguinal ring, which serves as an exit point for the spermatic cord in males and the round ligament in females. The posterior wall of the inguinal canal is primarily formed by the transversalis fascia, which covers the internal inguinal ring and the internal oblique muscle.

**Why the Correct Answer is Right:** In the anatomy of the inguinal canal, the posterior wall is primarily composed of the transversalis fascia, which is a thin, flat sheet of connective tissue. This sheet covers the internal inguinal ring (formed by the confluence of the internal inguinal ring and the posterior aspect of the internal oblique muscle) and the internal oblique muscle.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** The longus colli muscle is not a component of the inguinal canal's posterior wall. It is a muscle on the ventral (anterior) side of the neck, not related to the abdominal wall structures.

B. **Option B:** The sartorius muscle is another muscle on the anterior aspect of the thigh, not involved in the formation of the inguinal canal posterior wall.

C. **Option C:** The pectineus muscle is an anterior thigh muscle and not part of the inguinal canal's posterior wall either.

D. **Option D:** The internal spermatic fascia is a thin layer of connective tissue covering the internal spermatic vessels (vena spermatica interna) and the internal spermatic nerve. It is located on the internal aspect of the spermatic cord, not involved in the formation of the inguinal canal posterior wall.

**Clinical Pearl:** Understanding the correct structure composition of the inguinal canal posterior wall is crucial for understanding the surgical procedures like Lichtenstein's repair for inguinal hernia repair. It helps in identifying potential complications and ensuring proper repair of the weak point in the abdominal wall.