**Core Concept**
Stria vascularis is a highly specialized epithelial structure found in the lateral wall of the cochlear duct in the inner ear. It plays a crucial role in the production and maintenance of the endolymphatic potential, which is essential for the normal functioning of the auditory system.

**Why the Correct Answer is Right**
The stria vascularis is a highly vascularized region rich in capillaries and melanocytes. It generates the endolymphatic potential through the action of the Na+/K+-ATPase pump and the K+ secretion mechanism. This potential difference is necessary for the normal functioning of the hair cells in the cochlear duct, which are involved in sound detection and processing. The stria vascularis is also responsible for the regulation of the ionic composition of the endolymph, which is critical for maintaining the normal functioning of the auditory system.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the stria vascularis is not found in the semicircular canals of the vestibular system, but rather in the cochlear duct of the auditory system.
**Option B:** This option is incorrect because the organ of Corti is a sensory epithelium that contains hair cells, but it is not responsible for generating the endolymphatic potential or regulating the ionic composition of the endolymph.
**Option C:** This option is incorrect because the Reissner's membrane is a thin layer of epithelial cells that separates the cochlear duct from the scala vestibuli, but it is not involved in the generation of the endolymphatic potential or the regulation of the ionic composition of the endolymph.

**Clinical Pearl / High-Yield Fact**
The stria vascularis is a highly specialized structure that is critical for the normal functioning of the auditory system. Damage to the stria vascularis can lead to hearing loss and other auditory disorders.

**Correct Answer: C. Cochlear duct.**