An organ not formed from ectoderm is

Options

A. Optic nerve
B. Middle ear
C. Inner ear
D. Skin.

Answer

To determine which organ is not formed from the ectoderm, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Germ Layers**:
- The human embryo has three primary germ layers: ectoderm, mesoderm, and endoderm. Each layer gives rise to different tissues and organs in the body.

2. **Identify the Role of Ectoderm**:
- The ectoderm is the outermost germ layer. It is responsible for forming several structures including:
- Skin
- Nervous system (including optic nerves)
- Hair and nails
- Enamel of teeth
- Epithelia of the eyes

3. **Analyze the Options**:
- The options provided are:
1. Optic nerve
2. Middle ear
3. Inner ear
4. Skin

4. **Evaluate Each Option**:
- **Optic Nerve**: Formed from ectoderm (incorrect option).
- **Middle Ear**: Formed from mesoderm (correct option).
- **Inner Ear**: Formed from ectoderm (incorrect option).
- **Skin**: Formed from ectoderm (incorrect option).

5. **Conclusion**:
- The only organ that is not formed from the ectoderm is the **middle ear**, which is formed from the mesoderm.

### Final Answer:
The organ not formed from ectoderm is the **middle ear**.

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