Match the structure with its developmental origin (germ layer).
| Column I | Column II |
|---|---|
| (a) Heart | (i) Ectoderm |
| (b) Limbs and digits | (ii) Mesoderm |
| (c) Hair and nails | (iii) Mesoderm |
| (d) Most major organ systems | (iv) Formed by the end of 12 weeks (first trimester) |