Assertion (A): Muscles of stomach wall possess thick layers of muscle fibers.
Reason (R): These muscles help in mixing the food with the enzymes present in the alimentary canal.

Options

A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true but R is NOT the correct explanation of A.
C. A is true but R is false.
D. A is false and R is true.

Explanation

To solve the question regarding the assertion and reason provided, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states: "Muscles of the stomach wall possess thick layers of muscle fibers."

- **Explanation**: The stomach wall is composed of several layers, including a muscular layer known as the muscularis. This layer is indeed made up of thick muscle fibers that are essential for the stomach's function. The thick muscle fibers enable the stomach to contract effectively, which is crucial for the mechanical digestion of food.

### Step 2: Analyze the Reason
The reason states: "These muscles help in mixing the food with the enzymes present in the alimentary canal."

- **Explanation**: The primary function of the stomach muscles is to mix the ingested food with gastric juices, which contain enzymes and acids that aid in digestion. This mixing action is vital for breaking down food into a semi-liquid form called chyme, which can then be further digested in the intestines. Thus, the reason correctly explains the function of the stomach muscles.

### Step 3: Determine the Relationship
Now we need to determine if the reason correctly explains the assertion.

- Since both the assertion and the reason are true, and the reason provides a correct explanation of why the stomach muscles are structured as they are, we conclude that the assertion and reason are both true, and the reason is a correct explanation of the assertion.

### Conclusion
Based on the analysis:
- **Assertion (A)** is true.
- **Reason (R)** is true and correctly explains (A).

Thus, the correct answer is: **Assertion and Reason are true, and Reason is a correct explanation of Assertion.**