**Core Concept**
Dilator papillae are small muscles in the iris that control the amount of light entering the eye by adjusting the size of the pupil. They are part of the iris sphincter and dilator muscle complex, which plays a crucial role in regulating the amount of light that enters the eye.

**Why the Correct Answer is Right**
The dilator papillae are supplied by the sympathetic nerves, which are part of the autonomic nervous system. The sympathetic nerves release the neurotransmitter norepinephrine, which stimulates the dilator papillae to contract and cause the pupil to dilate. This is an example of the sympathetic nervous system's role in increasing the diameter of the pupil, allowing more light to enter the eye.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the dilator papillae are not supplied by the parasympathetic nerves, which are responsible for decreasing the diameter of the pupil.
* **Option B:** This option is incorrect because the dilator papillae are not supplied by the somatic nerves, which control voluntary movements such as eye movements.
* **Option D:** This option is incorrect because the dilator papillae are not supplied by the parasympathetic nerves via the ciliary ganglion.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the sympathetic nerves control the dilator papillae, whereas the parasympathetic nerves control the sphincter papillae, which are responsible for constricting the pupil.

**Correct Answer: C. Sympathetic nerves. Sympathetic nerves.**