A 28-year-old primigravida is counseled about normal embryonic development. She is informed that the notochord, which appears during the second week of development, eventually regresses and gives rise to which of the following structures?

Explanation

## Notochord and Its Derivatives The notochord is a transient mesodermal structure that appears during the second week of development and plays a crucial role in induction and patterning of the embryo. ### Fate of the Notochord: - **Nucleus Pulposus**: The notochord gives rise to the nucleus pulposus of the intervertebral disc. This is the most clinically important derivative. - **Regression**: Most of the notochord regresses by the end of the embryonic period. - **Remnants**: Small remnants may persist as the **notochordal remnants**, which can occasionally give rise to chordomas (rare malignant tumors of the spine). ### Other Structures (NOT from notochord): - **Annulus fibrosus**: Derived from the sclerotomes of the somites (mesodermal origin, but NOT from notochord). - **Anterior and posterior longitudinal ligaments**: Derived from the ventral and dorsal mesodermal tissues surrounding the vertebral column, not from the notochord. **Key Point:** The notochord is a primary inducer during development and its primary derivative of clinical significance is the nucleus pulposus. This is a high-yield fact for NEET PG embryology.