Final answer:
The muscularis externa layer has two subdivisions: longitudinal muscle and circular muscle. It promotes mechanical digestion and helps move food along the canal.
Step-by-step explanation:
The muscularis externa layer in the wall of the alimentary canal has two major subdivisions: the longitudinal muscle and the circular muscle. The longitudinal muscle runs along the length of the GI tract organs, while the circular muscle encircles the lower GI tract organs. These muscles contract to facilitate peristalsis, which helps propel food through the digestive system.
The major functions of the muscularis externa layer include promoting mechanical digestion, exposing food to digestive chemicals, and moving food along the canal.