In snakes the locomotion is helped by

Options

A. ribs only
B. reduced ribs
C. reduced limbs
D. ribs and reduced limbs

Answer

### Step-by-Step Solution:

1. **Understanding Snake Anatomy**: Snakes have a unique skeletal structure that mainly consists of a skull, vertebrae, and ribs. They have very reduced or vestigial limbs, which means their limbs are not functional for locomotion.

2. **Types of Locomotion in Snakes**: Snakes exhibit various forms of locomotion, including:
- Rectilinear locomotion
- Lateral undulation
- Side winding
- Concertina movement
- Side pushing

3. **Focusing on Rectilinear Locomotion**: Among these, rectilinear locomotion is a significant method that snakes use to move. This type of movement is characterized by a straight-line motion, which is particularly useful for stealth.

4. **Muscle Involvement**: The rectilinear locomotion relies on two sets of muscles known as the costocutaneous muscles. These muscles are attached to the ribs and the skin. They work in opposition to create movement.

5. **Role of Ribs**: Although it was initially thought that the ribs themselves moved during locomotion, it has been clarified that the ribs remain stationary. Instead, the movement is generated by the contraction of the muscles and the skin, which allows the snake to glide forward.

6. **Conclusion**: Therefore, in snakes, locomotion is primarily assisted by the ribs, as they provide the structure for the muscles to act upon, even though the ribs themselves do not move.

### Final Answer:
In snakes, locomotion is helped by **ribs only**.