Which germ layer forms CNS?

Explanation

### Step-by-Step Solution:

1. **Understand the Germ Layers**: In embryonic development, there are three primary germ layers: ectoderm, mesoderm, and endoderm. Each of these layers differentiates into various tissues and organs in the body.

2. **Identify the Functions of Each Germ Layer**:
- **Ectoderm**: This layer primarily forms the nervous system and the outer layer of skin. It differentiates into epithelial and neural tissues.
- **Endoderm**: This layer forms the lining of the gastrointestinal tract and associated structures, such as the esophagus, trachea, and intestines.
- **Mesoderm**: This layer gives rise to muscles, bones, and connective tissues.
...