During embryonic development in most vertebrates, the notochord is replaced by which structure?

During embryonic development in most vertebrates, the notochord is replaced by which structure?

• A. Dorsal nerve cord
• B. Pharyngeal arches
• C. A rigid external exoskeleton
• D. The vertebral column replaces the notochord as axial support

Answer: (D)

In vertebrate development, the axial support shifts from the notochord to the vertebral column. The notochord is a flexible rod along the body axis that provides structural support and signals tissue patterns early on. As development proceeds, the surrounding somites form vertebrae that ossify and enclose the notochord, so the vertebral column takes over as the main axial support. The notochord itself is largely replaced, though remnants can remain as the nucleus pulposus inside intervertebral discs. This is different from the dorsal nerve cord, which develops from the neural tube, or from pharyngeal arches, which contribute to head and throat structures. An external exoskeleton isn’t typical of vertebrates either.

In vertebrate development, the axial support shifts from the notochord to the vertebral column. The notochord is a flexible rod along the body axis that provides structural support and signals tissue patterns early on. As development proceeds, the surrounding somites form vertebrae that ossify and enclose the notochord, so the vertebral column takes over as the main axial support. The notochord itself is largely replaced, though remnants can remain as the nucleus pulposus inside intervertebral discs. This is different from the dorsal nerve cord, which develops from the neural tube, or from pharyngeal arches, which contribute to head and throat structures. An external exoskeleton isn’t typical of vertebrates either.