Final answer:
The muscularis of the stomach is composed of three smooth muscle layers: circular, oblique, and longitudinal. The oblique layer helps with the churning and mixing of food, aiding in mechanical digestion.
Step-by-step explanation:
The muscularis of the stomach is composed of three smooth muscle layers: an inner circular layer, a middle oblique layer, and an outer longitudinal layer. The addition of the oblique muscle layer allows the stomach to vigorously churn and mix food, aiding in mechanical digestion. The contractions of these muscle layers help move food along the stomach's canal.