**Core Concept**
The orbital septum is a fibrous layer that forms the anterior boundary of the orbit. It is a critical anatomical structure that separates the orbit from the facial soft tissues and helps maintain the integrity of the eye.

**Why the Correct Answer is Right**
The orbital septum is formed by the fusion of the orbital fascia and the periosteum of the orbital bones. This fusion creates a strong, fibrous layer that is continuous with the periosteum of the frontal bone, the zygomatic bone, and the maxillary bone. The orbital septum plays a crucial role in preventing the protrusion of orbital contents into the facial soft tissues and maintaining the normal anatomy of the orbit.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the orbital septum is not formed by the lacrimal gland.
* **Option B:** This option is incorrect because the orbital septum is not formed by the levator palpebrae superioris muscle.
* **Option C:** This option is incorrect because the orbital septum is not formed by the orbital fat.

**Clinical Pearl / High-Yield Fact**
The orbital septum is a critical anatomical structure that is often involved in orbital fractures and cellulitis. It is essential for surgeons and clinicians to have a thorough understanding of the anatomy of the orbital septum to diagnose and manage these conditions effectively.

**Correct Answer:** D. The orbital septum is formed by the fusion of the orbital fascia and the periosteum of the orbital bones.