**Core Concept**
The vitreous is a clear gel-like substance in the eye, comprising of 98% water and 2% collagen and hyaluronic acid. The vitreous is categorized into three zones based on its composition and structure: the pre-vitreous, the vitreous body, and the post-vitreous.

**Why the Correct Answer is Right**
The tertiary vitreous, also known as the **hyaloid artery remnant**, is a fibrovascular structure that remains in the center of the vitreous body. It is formed from the remnants of the hyaloid artery, which supplies the developing lens and vitreous during embryonic development. The hyaloid artery typically atrophies and obliterates by the 4th to 8th week of gestation, leaving behind a fibrovascular structure known as the tertiary vitreous.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the classification of the vitreous.
**Option B:** This option is incorrect as it does not accurately describe the tertiary vitreous.
**Option D:** This option is incorrect as it does not accurately describe the tertiary vitreous.

**Clinical Pearl / High-Yield Fact**
The presence of the hyaloid artery remnant or tertiary vitreous can be an important diagnostic clue in conditions such as persistent fetal vasculature or retinopathy of prematurity.

**Correct Answer: C. Hyaloid artery remnant.**