Question

Seeing pulsation of the artery at the completion of this dissection.
1. This is a run-on that can be fixed with a period.
2. This is a run-on that can be fixed by adding a comma and a conjunction.
3. This is a fragment that can be fixed by adding a subject and verb after this long introductory element.
4. This is a fragment that can be fixed by removing the word seeing from the beginning of the sentence.
5. The sentence is fine as it is.

Answer 1

Seeing pulsation of the artery at the completion of this dissection, I ran.

so #3.