**Core Concept**
A "blow-out" fracture of the orbit is a type of orbital fracture characterized by the displacement of the orbital floor or medial wall due to increased intraorbital pressure, typically resulting from a direct blow to the globe or orbit. This condition often involves the entrapment of orbital contents, such as the inferior rectus muscle or fat, within the fractured bony orbit.

**Why the Correct Answer is Right**
The correct answer involves the fracture of the orbital floor, which is the most common location for a blow-out fracture. This occurs due to the thinness and weakness of the orbital floor, which can be easily disrupted by a direct blow to the globe. The inferior rectus muscle is often entrapped within the fractured floor, leading to limited eye movement and other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Fracture of the orbital roof is incorrect because the orbital roof is a thick, strong bony structure that is not prone to blow-out fractures.
**Option B:** Fracture of the zygomatic arch is incorrect because while the zygomatic arch can be involved in orbital fractures, it is not typically the site of a blow-out fracture.
**Option C:** Fracture of the maxillary bone is incorrect because while the maxillary bone forms part of the orbital floor, a blow-out fracture typically involves the orbital floor as a whole, not just the maxillary bone.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the presence of enophthalmos (posterior displacement of the globe) and limited eye movement, particularly downward gaze, are key clinical signs of a blow-out fracture of the orbit.

**Correct Answer: C. Fracture of the orbital floor.**