## Notochord Derivatives The **notochord** is a transient mesodermal structure that appears during the second week of development and plays a crucial role in embryonic induction. ### Key Derivatives: - **Nucleus pulposus**: The notochord degenerates but its remnants form the nucleus pulposus of the intervertebral disc. This is the primary notochordal derivative. - **Notochordal remnants**: May persist as a **chordoma** (a rare malignant tumor) if notochordal cells persist abnormally. ### What the Notochord Does NOT Form: - **Vertebral bodies**: Derived from sclerotomes (paraxial mesoderm) - **Anterior/posterior longitudinal ligaments**: Derived from mesoderm (connective tissue) - **Spinal cord**: Derived from ectoderm (neuroectoderm) **Clinical Pearl:** Chordomas are rare malignant tumors arising from notochordal remnants, typically occurring at the sacrococcygeal region or sella turcica. **High-Yield:** The notochord is the key inductive tissue for neural tube and somite formation, but its only significant adult derivative is the nucleus pulposus.
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