Final answer:
The superior esophageal sphincter is a thickened ring of circular skeletal muscle marking the area where the esophagus and the pharynx meet.
Step-by-step explanation:
At the superior end of the esophagus, the superior esophageal sphincter is a thickened ring of __________ muscle marking the area where the esophagus and the pharynx meet-
- circular smooth
- circular skeletal
- longitudinal smooth
- longitudinal skeletal
Based on the provided information, the correct answer is
circular skeletal
muscle. The upper two-thirds of the esophagus consists of both smooth and skeletal muscle fibers, and the superior esophageal sphincter is located at the area where the esophagus and the pharynx meet. It serves as a valve to control the movement of food from the pharynx into the esophagus.