**Core Concept**
Nasopharyngeal chordoma is a rare, slow-growing malignant tumor that arises from the embryonic notochord remnant. This concept is crucial in understanding the origin of chordomas, which can occur in various midline locations, including the spheno-occipital region and the clivus.

**Why the Correct Answer is Right**
Chordomas arise from the notochord, a precursor to the spine that eventually fuses with the vertebral bodies. In the case of nasopharyngeal chordomas, they originate from the remnant notochord cells that persist in the midline of the skull base. The notochord is an embryonic structure that gives rise to the nucleus pulposus of the intervertebral discs and the centrum of the vertebrae.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is vague and does not specify a particular embryonic structure. While it's true that chordomas arise from embryonic remnants, notochord is the specific precursor to chordomas.
**Option B:** This option is incorrect because the sphenoid bone is a component of the skull base but not the origin of nasopharyngeal chordomas.
**Option C:** This option is incorrect because the cartilaginous structures of the skull base, such as the nasal septum, are not the origin of nasopharyngeal chordomas.

**Clinical Pearl / High-Yield Fact**
Chordomas are typically slow-growing and can cause symptoms due to local destruction of surrounding structures, such as cranial nerves, sinuses, and the nasal cavity. A high index of suspicion is necessary for early diagnosis, as these tumors can be challenging to distinguish from other skull base lesions.

**Correct Answer:** C. Remnant notochord cells.