## **Core Concept**
The third cranial nerve, also known as the oculomotor nerve, is responsible for controlling several eye muscles, including the medial rectus, superior rectus, inferior rectus, and inferior oblique, as well as the levator palpebrae superioris muscle, which elevates the eyelid. Third nerve palsy, or oculomotor nerve palsy, results in weakness or paralysis of these muscles, leading to characteristic clinical features.

## **Why the Correct Answer is Right**
The correct answer, ptosis, is indeed a feature of third nerve palsy due to the involvement of the levator palpebrae superioris muscle. Other features include:
- Down and out position of the eye (due to the unopposed action of the lateral rectus and superior oblique muscles)
- Dilated pupil (if the parasympathetic fibers are involved)
- Limited or absent adduction, elevation, and depression of the eye

## **Why Each Wrong Option is Incorrect**
- **Option A:** Ptosis is a feature of 3rd nerve palsy; thus, it's not the correct answer to the question about which is NOT a feature.
- **Option B:** A dilated pupil can be a feature of third nerve palsy, especially if the palsy is due to an aneurysm or other compressive lesion affecting the nerve's parasympathetic fibers.
- **Option C:** Limitation of gaze in all directions except laterally is consistent with third nerve palsy, making it a feature rather than an exception.

## **Option D:**
- **Option D:** The correct answer provided is related to the absence of a particular symptom. Since ptosis (Option A) and other listed features (like pupil dilation and limited eye movements) are characteristic of third nerve palsy, the exception or the one that does not fit with typical features needs clarification based on standard clinical presentations.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that in a diabetic third nerve palsy, the pupil is typically spared (not dilated), which helps differentiate it from third nerve palsy caused by an aneurysm or other compressive lesions where the pupil is often involved.

## **Correct Answer: D.**