**Core Concept**
The nasolacrimal duct is a crucial structure in the lacrimal apparatus, responsible for draining tears from the eye into the nasal cavity. Its proper anatomy and direction are essential for understanding the pathophysiology of lacrimal disorders and the effectiveness of surgical interventions.

**Why the Correct Answer is Right**
The nasolacrimal duct is a curved tube approximately 12 mm in length, originating from the lacrimal sac and traversing the bony orbit to open into the nasal cavity. Its direction is posteriorly and inferiorly, forming a 90-degree angle with the lacrimal sac. This anatomical configuration allows tears to flow from the eye into the nasal cavity through gravity-assisted drainage. The duct's direction is also influenced by the surrounding bony structures, including the lacrimal fossa and the maxillary bone.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the nasolacrimal duct does not ascend to the forehead. Its course is actually downward and backward.
**Option B:** This option is incorrect as the nasolacrimal duct does not open into the oral cavity. Instead, it opens into the nasal cavity through the inferior meatus.

**Clinical Pearl / High-Yield Fact**
The direction of the nasolacrimal duct is crucial for understanding the pathophysiology of epiphora (excessive tearing) and dacryocystitis (inflammation of the lacrimal sac). A blockage in the nasolacrimal duct can lead to tearing and facial pain, highlighting the importance of proper anatomical knowledge in clinical practice.

**Correct Answer: C. Posteriorly and inferiorly**