**Core Concept**
Schatzki's ring is a type of esophageal ring that forms at the squamocolumnar junction in the esophagus, typically causing dysphagia. It is a narrow, annular mucosal ring that can lead to intermittent or progressive dysphagia, depending on its severity. This condition is often associated with a concomitant hiatal hernia.

**Why the Correct Answer is Right**
Schatzki's ring forms at the squamocolumnar junction in the esophagus due to chronic irritation and inflammation of the mucosa, leading to fibrosis and scarring. This results in the narrowing of the esophageal lumen, causing symptoms of dysphagia. The squamocolumnar junction is the area where the squamous epithelium of the esophagus meets the columnar epithelium of the stomach, and it is a common site for the development of Schatzki's ring.

**Why Each Wrong Option is Incorrect**
**Option A:** The upper end of the esophagus is not a typical location for Schatzki's ring, as it is more commonly associated with the lower end of the esophagus, near the squamocolumnar junction.

**Option B:** The mid-esophagus is not a specific location for Schatzki's ring, as it can occur anywhere along the length of the esophagus, but it is most commonly found near the squamocolumnar junction.

**Option D:** The fundus of the stomach is not a location for Schatzki's ring, as it is a condition that affects the esophagus, not the stomach.

**Clinical Pearl / High-Yield Fact**
Schatzki's ring is often associated with a concomitant hiatal hernia, and patients with this condition may also experience symptoms of gastroesophageal reflux disease (GERD).

**✓ Correct Answer: C. Squamocolumnar junction in esophagus**