**Core Concept**
The pharyngeal plexus is a complex network of nerves that supplies the muscles of the pharynx, providing motor innervation and sensation to this region. It is formed by the convergence of branches from the vagus nerve (cranial nerve X) and the glossopharyngeal nerve (cranial nerve IX).

**Why the Correct Answer is Right**
The stylopharyngeus muscle, which is responsible for elevating the pharynx and larynx during swallowing, is unique in that it is the only muscle of the pharynx that is not supplied by the pharyngeal plexus. Instead, it is innervated by the glossopharyngeal nerve (cranial nerve IX) via its pharyngeal branch. This distinct innervation is a result of the stylopharyngeus muscle's embryological origin from the third pharyngeal arch.

**Why Each Wrong Option is Incorrect**
**Option A:** The inferior constrictors are indeed supplied by the pharyngeal plexus, which receives contributions from the vagus nerve and the glossopharyngeal nerve.
**Option B:** The salpingopharyngeus muscle, which assists in elevating the pharynx and larynx during swallowing, is also supplied by the pharyngeal plexus.
**Option D:** Since the stylopharyngeus muscle is the correct exception, this option is incorrect.

**Clinical Pearl / High-Yield Fact**
The pharyngeal plexus is a critical structure in the pharynx, and its disruption can lead to significant consequences, including difficulty swallowing (dysphagia) and impaired sensation in the pharyngeal region.

**✓ Correct Answer: C. Stylopharyngeus**