**Core Concept**
The submandibular gland is a major salivary gland located under the mandible, playing a crucial role in saliva production and secretion. Its innervation is vital for regulating salivary function and is typically derived from the parasympathetic nervous system.

**Why the Correct Answer is Right**
The submandibular gland receives its parasympathetic secretomotor fibers from the submandibular ganglion, which is a parasympathetic ganglion located near the submandibular gland. These fibers arise from the inferior salivatory nucleus in the medulla oblongata and synapse in the submandibular ganglion before reaching the submandibular gland. The preganglionic fibers are part of the facial nerve (cranial nerve VII), which carries both motor and sensory fibers to the submandibular ganglion.

**Why Each Wrong Option is Incorrect**
* **Option A:** The submandibular gland does not receive its primary innervation from the glossopharyngeal nerve (cranial nerve IX), which is responsible for the parasympathetic innervation of the parotid gland.
* **Option B:** The trigeminal nerve (cranial nerve V) is primarily responsible for sensory innervation of the face, including the submandibular gland area, but it does not provide the secretomotor fibers necessary for salivary gland function.
* **Option D:** The hypoglossal nerve (cranial nerve XII) is a motor nerve that controls tongue movement and is not responsible for the innervation of the submandibular gland.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the submandibular gland receives its secretomotor innervation from the facial nerve via the submandibular ganglion, making the facial nerve crucial for salivary gland function in this area.

**Correct Answer: C. The facial nerve via the submandibular ganglion.**