**Core Concept**
The hippocampal formation is a critical component of the temporal lobe, playing a key role in **memory formation** and **spatial navigation**. It consists of several structures that work together to facilitate these functions. The primary structures included in the hippocampal formation are the **hippocampus proper**, the **dentate gyrus**, and the **subiculum**.

**Why the Correct Answer is Right**
To determine the correct answer, we must identify which of the given options is not a part of the hippocampal formation. The hippocampal formation is primarily involved in the process of **consolidating information from short-term memory to long-term memory**, and its components are anatomically and functionally linked to achieve this.

**Why Each Wrong Option is Incorrect**
**Option A:**
**Option B:**
**Option C:**
Given the lack of specific options, it's essential to recognize that the hippocampal formation does not include structures outside its defined anatomical boundaries, such as certain adjacent cortical areas or other brain regions not directly involved in its primary functions.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that damage to the hippocampal formation, such as in **Alzheimer's disease**, can lead to significant impairments in forming new memories, a condition known as **anterograde amnesia**.

**Correct Answer:** D. Amygdala