Notochord, skeletal system and dermis of
the skin are the derivatives of

Options

A. endoderm
B. ectoderm
C. mesoderm
D. all the three layers

Answer

To determine the derivatives of the notochord, skeletal system, and dermis of the skin, we need to understand the three germ layers formed during embryogenesis: ectoderm, mesoderm, and endoderm.

### Step-by-Step Solution:

1. **Identify the Germ Layers**:
- During embryogenesis, three primary germ layers are formed: ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer).

2. **Understand the Functions of Each Germ Layer**:
- **Ectoderm**: This layer forms the outermost layer of the body, including the skin and nervous system.
- **Mesoderm**: This middle layer gives rise to various structures, including the skeletal system, muscles, and dermis of the skin.
- **Endoderm**: This innermost layer primarily forms the lining of the gastrointestinal tract and associated organs.

3. **Analyze the Derivatives**:
- **Notochord**: This structure is a mesodermal derivative that provides support and is located beneath the nerve cord.
- **Skeletal System**: The bones and cartilage of the skeletal system are derived from the paraxial mesoderm.
- **Dermis of the Skin**: The dermis, which is the inner layer of the skin, is also derived from the mesoderm.

4. **Conclusion**:
- Since the notochord, skeletal system, and dermis of the skin all arise from the mesoderm, the answer to the question is **mesoderm**.

### Final Answer:
The notochord, skeletal system, and dermis of the skin are derivatives of the **mesoderm**.