**Core Concept**
The submandibular gland is a major salivary gland located beneath the mandible, and its anatomical structure is divided into two parts: the superficial and deep lobes. The superficial lobe is located lateral to the mylohyoid muscle, while the deep lobe is situated medial to it.

**Why the Correct Answer is Right**
The mylohyoid muscle is a thin, flat muscle that forms the floor of the oral cavity and separates the submandibular gland into its superficial and deep parts. This muscle plays a crucial role in elevating the hyoid bone and the larynx during swallowing. The mylohyoid muscle is also an important landmark for the surgical approach to the submandibular gland, as it helps to identify the gland's superficial and deep lobes. The mylohyoid muscle is innervated by the mylohyoid nerve, a branch of the mandibular division of the trigeminal nerve.

**Why Each Wrong Option is Incorrect**
* **Option A:** The digastric muscle, which consists of two bellies separated by an intermediate tendon, is not directly related to the division of the submandibular gland into superficial and deep parts.
* **Option B:** The geniohyoid muscle, which is attached to the genial tubercle of the mandible and the body of the hyoid bone, is not involved in the division of the submandibular gland.
* **Option D:** The stylohyoid muscle, which is attached to the styloid process and the lesser horn of the hyoid bone, is not related to the division of the submandibular gland.

**Clinical Pearl / High-Yield Fact**
It is essential to identify the mylohyoid muscle during surgical procedures involving the submandibular gland to avoid injury to the gland's superficial and deep lobes. The mylohyoid muscle can be palpated during a submandibular gland dissection to ensure that the gland is not damaged.

**✓ Correct Answer: C. Mylohyoid**