**Core Concept**
In anterior dislocation of the shoulder, the humerus is displaced from the glenoid cavity of the scapula, resulting in a characteristic position of the arm. This position is often used as a clinical indicator of anterior dislocation.

**Why the Correct Answer is Right**
The arm in anterior dislocation of the shoulder is typically held in a position of abduction, external rotation, and medial (internal) rotation. This position occurs due to the displacement of the humerus and the resulting tension on the surrounding muscles and ligaments. The external rotation is caused by the pull of the supraspinatus and infraspinatus muscles, while the medial rotation is due to the pull of the subscapularis muscle.

**Why Each Wrong Option is Incorrect**
* **Option A:** This position is not typically associated with anterior dislocation of the shoulder.
* **Option B:** The arm in posterior dislocation of the shoulder is usually positioned in adduction, internal rotation, and medial rotation.
* **Option D:** This position is not a characteristic feature of anterior dislocation of the shoulder.

**Clinical Pearl / High-Yield Fact**
In anterior dislocation of the shoulder, the characteristic position of the arm is often remembered using the mnemonic "ABCD": Abduction, External Rotation, Medial Rotation, and Displacement. This helps to quickly identify the position of the arm in anterior dislocation.

**Correct Answer: C.**