Notochord has been replaced in vertebrates by

Options

A. Brain and spinal cord
B. Cranium and vertebral column
C. Post anal tail
D. Both A and B

Answer

To answer the question "Notochord has been replaced in vertebrates by," we can follow these steps:

### Step 1: Understand the Role of Notochord
The notochord is a flexible rod-like structure that is present in the embryonic development of vertebrates. It plays a crucial role in providing structural support and is involved in the development of the nervous system, particularly the neural tube.

**Hint:** Recall that the notochord is significant during embryonic development and supports the body structure.

### Step 2: Identify What Replaces the Notochord
In vertebrates, the notochord is eventually replaced by more complex structures. Specifically, it is replaced by the vertebral column (spine) and the cranium (skull). These structures provide a more rigid framework for the body and protect the central nervous system.

**Hint:** Think about the skeletal structures that provide support and protection in vertebrates.

### Step 3: Analyze the Options Given
The options provided are:
1. Brain and spinal cord
2. Cranium and vertebral column
3. Post and anal tail
4. Both A and B

From our understanding, the correct replacement of the notochord in vertebrates is the cranium and vertebral column.

**Hint:** Focus on the structures that are directly related to the skeletal system in vertebrates.

### Step 4: Conclusion
Thus, the correct answer to the question is that the notochord in vertebrates is replaced by the cranium and vertebral column.

**Final Answer:** Cranium and vertebral column.