## Core Concept
The tongue is primarily composed of intrinsic and extrinsic muscles. The intrinsic muscles of the tongue are responsible for its shape and movement. Among these, one muscle is notably described as fan-shaped and forms the main bulk of the tongue.

## Why the Correct Answer is Right
The **Genioglossus** muscle is one of the extrinsic muscles of the tongue but also contributes significantly to its bulk. However, when referring to the intrinsic muscles that give the tongue its shape, the **Intrinsic muscles** are key. Among the intrinsic muscles, the **Transverse, Longitudinal, and Vertical muscles** are distinguished. Specifically, the **Vertical muscle of the tongue** is described as being fan-shaped and plays a crucial role in altering the tongue's shape and size.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, without specifying the muscle, we cannot directly assess its accuracy.
- **Option B:** Similarly, this option lacks specificity but can be considered incorrect if it does not accurately represent the fan-shaped muscle.
- **Option C:**
- **Option D:** This option is incorrect if it refers to any muscle other than the one described as fan-shaped and primarily forming the bulk of the tongue.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **intrinsic muscles of the tongue** allow for its various movements and changes in shape. Among these, the **vertical muscle** is specifically noted for its fan-shaped appearance and significant contribution to the tongue's bulk. This muscle's action helps in flattening and broadening the tongue.

## Correct Answer: B. Vertical muscle of tongue