## **Core Concept**
The submandibular salivary gland is divided into a superficial and a deep part. The deep part of the gland is closely related to specific structures in the neck, particularly those involved in the passage of nerves and vessels.

## **Why the Correct Answer is Right**
The deep part of the submandibular gland is situated between the mylohyoid muscle and the mandible. It is closely related to the **lingual nerve**, which supplies sensation to the anterior two-thirds of the tongue. The gland also has a relationship with the **hypoglossal nerve (cranial nerve XII)**, which provides motor innervation to the tongue. The correct answer highlights the intimate relationship of the deep part of the submandibular gland with the **hypoglossal nerve**.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although the mylohyoid nerve does relate to the submandibular gland (as it supplies the mylohyoid muscle and the anterior belly of the digastric muscle), it is not specifically known for its close association with the deep part of the gland in the context provided.
- **Option B:** This option is incorrect as it does not accurately represent a structure closely associated with the deep part of the submandibular gland.
- **Option C:** This option might seem plausible due to the gland's location but does not accurately reflect the specific and significant relationship that the correct answer does.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the **lingual nerve** loops around the **submandibular duct (Wharton's duct)** and is closely associated with the deep part of the submandibular gland. During surgical procedures in this area, preserving these nerves is crucial to avoid nerve damage.

## **Correct Answer:** . hypoglossal nerve.