**Core Concept**
The esophagus is a muscular tube that propels food into the stomach through peristalsis. Maximum dilatation of the esophagus is a clinical phenomenon where the esophagus widens to accommodate large amounts of food or fluids.

**Why the Correct Answer is Right**
During maximum dilatation, the lower esophageal sphincter (LES) relaxes, allowing the esophagus to widen significantly. The cricopharyngeus muscle, which is the upper esophageal sphincter, also relaxes. This relaxation of the sphincters allows the esophagus to dilate and accommodate large volumes of food or fluids, preventing food from entering the airways. The esophageal musculature, particularly the longitudinal muscles, also plays a crucial role in this process by shortening and widening the esophagus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the cricopharyngeus muscle does not play a significant role in maximum dilatation of the esophagus. Instead, it is responsible for protecting the airway during swallowing.

**Option B:** This option is incorrect because the lower esophageal sphincter (LES) relaxation is a key factor in maximum dilatation, not contraction.

**Option C:** This option is incorrect because the striated muscle of the upper esophagus is involved in peristalsis, not maximum dilatation.

**Clinical Pearl / High-Yield Fact**
During maximum dilatation, the esophagus can widen up to 2-3 times its normal diameter, allowing it to accommodate large amounts of food or fluids. This phenomenon is often seen in conditions such as achalasia or diffuse esophageal spasm.

**Correct Answer: D. Lower esophageal sphincter relaxation.**