**Core Concept**
The glenohumeral joint is a ball-and-socket joint that allows for wide range of motion in various directions. However, this mobility comes at the cost of stability, making it prone to dislocations. In order to prevent posterior dislocation of the glenohumeral joint, the surrounding muscles and ligaments must provide adequate support and restraint.

**Why the Correct Answer is Right**
The coracobrachialis muscle plays a crucial role in preventing posterior dislocation of the glenohumeral joint. This muscle originates from the coracoid process of the scapula and inserts into the medial aspect of the humerus. As the arm is lifted, the coracobrachialis muscle contracts, pulling the humerus forward and preventing it from dislocating posteriorly. This action is particularly important when lifting heavy objects, such as a suitcase, where the force of the movement can cause the humerus to dislocate posteriorly.

**Why Each Wrong Option is Incorrect**
**Option A:** The deltoid muscle is primarily responsible for shoulder abduction and flexion, but it does not play a significant role in preventing posterior dislocation of the glenohumeral joint.

**Option B:** The latissimus dorsi muscle is a powerful muscle that extends, adducts, and medially rotates the shoulder joint, but it is not primarily responsible for preventing posterior dislocation.

**Option D:** The supraspinatus muscle is responsible for initial abduction of the shoulder joint, but it does not play a significant role in preventing posterior dislocation.

**Clinical Pearl / High-Yield Fact**
When lifting heavy objects, it is essential to engage the coracobrachialis muscle to prevent posterior dislocation of the glenohumeral joint. This can be achieved by keeping the arm close to the body and lifting with the legs rather than the back.

**✓ Correct Answer: C. Coracobrachialis**