A 32-year-old pregnant woman undergoes routine ultrasound at 12 weeks gestation. The sonographer notes normal development of the embryo. Which of the following structures is derived from the notochord?

Explanation

## Notochord and Its Derivatives The **notochord** is a mesodermal structure that appears during the 3rd week of development and plays a crucial role in embryogenesis. ### Key Derivatives of the Notochord: - **Nucleus pulposus** of intervertebral discs — the remnant of the notochord persists in the center of each disc - **Coccygeal body** (coccygeal vertebra) — a small remnant at the tip of the coccyx ### Clinical Pearl: The notochord degenerates in most regions but persists as the nucleus pulposus. This is why chordomas (rare malignant tumors) arise along the midline from notochordal remnants — most commonly in the sacrococcygeal region and less frequently in the spheno-occipital region. ### Embryological Origin of Other Spinal Structures: - **Vertebral bodies and arches**: Sclerotomes (mesodermal origin from somites) - **Anterior and posterior longitudinal ligaments**: Derived from mesoderm (not notochord) - **Dura mater**: Derived from neural crest cells and mesoderm **High-Yield:** The nucleus pulposus is the ONLY major adult structure derived from the notochord.