**Core Concept**
Keisselbach's plexus is an anastomotic network of blood vessels in the anterior part of the hard palate, connecting the two sides of the nasal septum. This plexus plays a crucial role in the blood supply of the nasal septum and is clinically significant due to its potential for bleeding.

**Why the Correct Answer is Right**
Keisselbach's plexus is present at the anterior part of the hard palate, specifically in the region of the incisive foramen and the nasal septum. This plexus is a vital anastomotic network that connects the sphenopalatine artery (anterior nasal branch) with the greater palatine artery (greater palatine branch). The presence of this plexus is essential for understanding the pathophysiology of epistaxis (nosebleeds), particularly in cases where the bleeding originates from the anterior part of the nasal septum.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because Keisselbach's plexus is specifically located in the anterior part of the hard palate, not in the posterior part.
* **Option B:** Incorrect because the plexus is not located in the nasal cavity itself, but rather in the anterior part of the hard palate, which lies above the nasal cavity.
* **Option C:** Incorrect because this option does not accurately describe the location of Keisselbach's plexus.

**Clinical Pearl / High-Yield Fact**
Keisselbach's plexus is a common source of anterior epistaxis (nosebleeds), and its presence should be considered when evaluating patients with bleeding from the anterior part of the nasal septum.

**Correct Answer:** C.