Which of these structures is found in the stomach but nowhere else in the alimentary canal?

a. an oblique muscle layer
b. a lining of columnar epithelium
c. a circular muscle layer
d. mucus-forming cells

A. an oblique muscle layer  

Explanation:

The alimentary canal has four main layers:

Mucosa (innermost layer which surrounds the lumen), submucosa (connective tissue with blood vessels, lymphatics, and nerves), muscular layer, serosa ( outermost layer of connective tissue).

Muscular layer is subdivided into:

•the inner- arranged in circular rings, prevents food from travelling backward  

•  outer layer- arranged longitudinally,  shortens the tract.

The stomach has an extra layer called inner oblique muscular layer (churning function).