On the basis of development, odontoid process of axis of mammals is

Options

A. Ribs of axis vertebra
B. Centrum of atlas
C. Neural spine of atlas
D. Centrum of axis.

Explanation

### Step-by-Step Solution:

1. **Understanding the Odontoid Process**: The odontoid process, also known as the dens, is a bony projection that arises from the axis vertebra (the second cervical vertebra) in mammals. It plays a crucial role in the rotation of the head.

2. **Identifying the Origin**: The odontoid process originates from the central part of the axis vertebra. It is an upward-projecting structure that allows for the articulation with the atlas (the first cervical vertebra).

3. **Developmental Basis**: When considering the development of the odontoid process, it is important to note that it is derived from the centrum of the atlas vertebra. This means that during the embryonic development, the odontoid process is formed from the material that makes up the centrum of the atlas.

4. **Evaluating the Options**: The question provides several options:
- Ribs of axis vertebrae
- Centrum of atlas
- Neural spine of atlas
- Centrum of axis

Based on our understanding:
- The ribs of the axis vertebrae are not related to the odontoid process.
- The neural spine of the atlas does not contribute to the formation of the odontoid process.
- The centrum of axis is incorrect as the odontoid process arises from the atlas.

5. **Conclusion**: The correct answer is that the odontoid process of the axis of mammals is derived from the **centrum of atlas**.

### Final Answer:
The odontoid process of the axis of mammals is the **centrum of atlas**.

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