Submandibular gland is situated in:
The digastric triangle is subdivided into anterior and posterior parts by the stylomandibular ligament, which extends from the tip of the styloid process to the angle of the mandible. The posterior part of the triangle is continuous above with the parotid region.
Contents in the anterior part of the triangle:

Submandibular salivary gland.
Submandibular lymph nodes.
Hypoglossal nerve.
Facial vein (lies superficial to the gland).
Facial artery (lies deep to the gland).
Submental artery.
Mylohyoid nerve and vessels.

Contents in the posterior part of the triangle:

External carotid artery.
Carotid sheath and its contents.
Structures passing between the external and internal carotid arteries.
Digastric triangle
Carotid triangle
Muscular triangle
Deep to hyoglossus muscle