**Core Concept**
A blowout fracture of the orbit refers to a specific type of fracture that occurs when there is a sudden increase in pressure within the orbit, causing the bones to fracture outward. This typically involves the **thin bones** of the orbital floor and medial wall. The **maxillary sinus** and **ethmoid air cells** are adjacent to these bones.

**Why the Correct Answer is Right**
The correct answer is related to the **orbital floor**, which is the most common site for a blowout fracture due to its thinness and the fact that it is prone to **increased intraorbital pressure** from a blow to the globe of the eye. The **zygomatic bone** and **maxillary bone** form part of the orbital floor.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because the roof of the orbit is stronger and less prone to fracture.
**Option B:** This option might seem plausible but is not the most accurate description of a blowout fracture.
**Option D:** This is incorrect as the lateral wall of the orbit is thicker and less commonly involved in blowout fractures.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that a blowout fracture can lead to **entrapment of extraocular muscles**, particularly the inferior rectus muscle, resulting in **diplopia** (double vision) and **limited upward gaze**.

**Correct Answer:** D. floor of the orbit