The cervical vertebra called axis provids head with sideways rotation. This can be because

Options

A. It is articulated to skull through occipital condyles
B. it is fused with `1^(st)` vertebra atlas
C. it is joined through elastic pads of fibrocartilage with other vertebrae, which provide mobility
D. it contains odontoid process that fits into the odontoid canal of atlas.

Explanation

To answer the question about why the cervical vertebra called axis provides the head with sideways rotation, we can break down the explanation into the following steps:

### Step-by-Step Solution:

1. **Understanding the Vertebral Column**:
- The vertebral column, commonly known as the spine, is composed of 26 small bones called vertebrae, which are arranged serially.

2. **Classification of Vertebrae**:
- The vertebrae are categorized into different regions:
- **Cervical vertebrae** (7 in number) in the neck,
- **Thoracic vertebrae** (12 in number) associated with the chest,
- **Lumbar vertebrae** (5 in number) in the lower back,
- **Sacrum and coccyx**, which are formed by fused vertebrae.

3. **Identifying the Axis**:
- The axis is the second cervical vertebra, following the first cervical vertebra known as the atlas. The atlas articulates directly with the skull.

4. **Joint Types**:
- The joint between the atlas and the axis is a special type of synovial joint known as a **pivot joint**. This type of joint allows for rotational movement.

5. **Function of the Odontoid Process**:
- The axis contains a projection called the **odontoid process** (or dens), which fits into the odontoid canal of the atlas. This anatomical feature is crucial for enabling the head to rotate sideways.

6. **Conclusion**:
- The correct reason why the axis allows for sideways rotation of the head is due to the presence of the odontoid process, which forms a pivot joint with the atlas.

### Final Answer:
The cervical vertebra called axis provides the head with sideways rotation because it contains an odontoid process that fits into the odontoid canal of the atlas, forming a pivot joint.

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