**Core Concept**
The axilla is a complex region bounded by the pectoralis major, teres major, and latissimus dorsi muscles. The posterior wall of the axilla is formed by the scapula, subscapularis muscle, and the serratus anterior muscle. This anatomical structure is crucial for understanding the lymphatic drainage and surgical approaches in the axillary region.

**Why the Correct Answer is Right**
The posterior wall of the axilla is primarily formed by the scapula and the muscles attached to it, including the subscapularis and teres major. The scapula provides a bony structure that separates the axillary cavity from the posterior thoracic wall. The subscapularis muscle, a part of the rotator cuff, is also a significant contributor to the posterior wall. This anatomy is essential for surgeons performing axillary dissections and lymph node biopsies.

**Why Each Wrong Option is Incorrect**
**Option A:** While the pectoralis major muscle forms part of the anterior wall of the axilla, it is not a component of the posterior wall.
**Option B:** The latissimus dorsi muscle is located on the back and contributes to the posterior aspect of the thoracic wall but does not form the posterior wall of the axilla.
**Option C:** The serratus anterior muscle is involved in the anterior wall of the axilla and helps in its formation but is not a primary component of the posterior wall.

**Clinical Pearl / High-Yield Fact**
To remember the walls of the axilla, use the mnemonic: "P.T.L.S." - Pectoralis (anterior), Teres (posterior), Latissimus (lateral), and Subscapularis (medial).

**Correct Answer:** C. Latissimus dorsi muscle.