**Core Concept**
The helix in a finger spring for mesial movement is a component of orthodontic mechanics used to achieve controlled tooth movement. It is a part of the edgewise appliance system, which utilizes a combination of archwires and springs to manipulate teeth in a specific direction.

**Why the Correct Answer is Right**
The helix is designed to provide a gentle, continuous force to the tooth, facilitating mesial movement. The spring is activated by placing the finger spring in a position that allows it to apply pressure to the helix, which in turn exerts a force on the tooth. The helix is typically positioned in a way that the force is directed mesially, allowing for controlled tooth movement.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the helix in a finger spring is not typically used for distal movement, which would require a different type of spring or appliance.
**Option B:** This option is incorrect because the helix is not a component of a lingual arch, which is a different type of orthodontic appliance used for different types of tooth movement.
**Option C:** This option is incorrect because the helix is not a part of a self-ligating bracket, which is a type of orthodontic bracket that uses a spring-loaded mechanism to hold the archwire in place.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the correct placement and activation of the helix in a finger spring are crucial for achieving the desired tooth movement. Improper placement or activation can lead to inadequate or even adverse effects on tooth movement.

**Correct Answer: C. The helix in a finger spring lies in the mesial aspect of the finger spring for mesial movement.**