**Core Concept**
The mastoid antrum is a cavity in the mastoid process of the temporal bone that serves as a connection between the middle ear and the mastoid air cells. Its anatomy is crucial for understanding the spread of infection and the development of complications in otitis media.

**Why the Correct Answer is Right**
The mastoid antrum does indeed communicate with the middle ear, specifically through the aditus ad antrum, which is a narrow passageway that connects the middle ear cavity to the mastoid antrum. This communication allows for the spread of infection and the development of mastoiditis. The mastoid antrum is also connected to the mastoid air cells, which are a network of air-filled cavities in the mastoid process.

**Why Each Wrong Option is Incorrect**
**Option A:** The thickness of the bone of the lateral wall of the mastoid antrum is actually about 1-2 mm, not 1.5 cm. This is a critical distinction, as the thin bone of the lateral wall makes it susceptible to erosion and damage during mastoiditis.

**Option C:** Air cells are indeed present in the mastoid process, but they are not limited to the upper part. The mastoid air cells are a network of air-filled cavities that can be found throughout the mastoid process, not just in the upper part.

**Option D:** The surface marking of the mastoid antrum is indeed done by the McEwen's triangle, which is a triangular area on the posterior aspect of the temporal bone. This triangle is formed by the intersection of the posterior root of the zygomatic arch, the temporal line, and the supramastoid crest.

**Clinical Pearl / High-Yield Fact**
The mastoid antrum is a critical structure in otolaryngology, and its anatomy is essential for understanding the spread of infection and the development of complications in otitis media. Remember that the mastoid antrum communicates with the middle ear, and its thin lateral wall makes it susceptible to erosion and damage during mastoiditis.

**✓ Correct Answer: B. It does not communicate with middle ear**