Final answer:
The striated muscles of the esophagus develop from the embryonic mesoderm. The upper third consists of striated (skeletal) muscle transitioning to smooth muscle in the lower two-thirds, which aids in peristalsis.
Step-by-step explanation:
The striated muscles of the esophagus are crucial in the process of swallowing or deglutition. They develop from the embryonic mesoderm, which differentiates into various muscle tissue types including skeletal muscle. The upper one-third of the esophagus contains striated (skeletal) muscle fibers, which are under voluntary control and contribute to the initiation of the swallowing process. These fibers transition to smooth muscle in the lower two-thirds of the esophagus, which is under involuntary control and responsible for the continued peristalsis that moves food through to the stomach.
In histological terms, the muscularis layer of the esophagus changes according to location: it starts as skeletal muscle, transitions into a combination of both skeletal and smooth muscle in the middle third, and ends up as smooth muscle in the lower third. The transition from skeletal to smooth muscle aids in the progression of the peristaltic waves that ensure the movement of the food bolus toward the stomach.