Final answer:
The innermost serosa (option D) is not a layer of the stomach wall because the serosa is actually the outermost layer of the alimentary canal's walls, and there is no layer called the innermost serosa in the stomach's anatomy.
Step-by-step explanation:
The question asks which of the listed layers is not a layer of the stomach wall. It is important to understand the structure of the stomach's wall to answer this question. According to the provided information, the stomach wall consists of multiple layers, including the mucosa, submucosa, muscularis, and serosa. The serosa layer is the outermost layer of the alimentary canal's walls and is present in the abdominal cavity. It lies superficial to the muscularis, which itself consists of three muscle layers -- the circular, longitudinal, and oblique muscle layers. The oblique muscle is unique to the stomach and aids in the mechanical mixing of food.
Given the layers that comprise the wall of the stomach, we can conclude that option D, "The innermost serosa," is the incorrect choice, as there is no such layer known as the innermost serosa. The serosa is always the outermost layer; thus, 'innermost serosa' is not applicable to the anatomy of the stomach.