Which of the following statements is correct?

Options

A. The soft substance present inside the bones is called bone marrow.
B. Pivot joint allows the maximum movement in all planes whereas hinge joint allows the least movement in one plane only.
C. The only movable bone in skull is the upper jaw bone.
D. Snakes have hollow bones and birds have flexible backbones.

Explanation

To determine which statement is correct, let's analyze each option step by step:

1. **Statement 1**: "The soft substance present inside the bones is called bone marrow."
- This statement is true. Bone marrow is indeed the soft tissue found inside bones, responsible for producing blood cells.

2. **Statement 2**: "The pivot joint allows maximum movement in all planes."
- This statement is incorrect. The pivot joint allows rotational movement, but not in all planes. The ball and socket joint is the one that allows maximum movement in all directions.

3. **Statement 3**: "The only movable bone in the skull is the upper jaw."
- This statement is also incorrect. The only movable bone in the skull is the lower jaw (mandible), not the upper jaw.

4. **Statement 4**: "Snakes have hollow bones whereas birds have flexible back bones."
- This statement is incorrect. Birds have hollow bones to reduce weight for flight, while snakes have flexible backbones that allow for their slithering movement.

**Conclusion**: The correct statement among the options is Statement 1: "The soft substance present inside the bones is called bone marrow."