* Mayo retractor: A type of surgical retractor used to hold back tissues and organs during surgery. It comes in various sizes and shapes, and is usually made of metal.
* Collins retractor: This term is not a recognized surgical retractor. There might be a less common retractor with a similar name or you might be thinking of a different instrument entirely.
To help me understand what you're looking for, please provide more context:
* What type of surgery are you interested in?
* Can you describe the retractor you're looking for? (e.g., its shape, size, purpose, etc.)
* Did you see this term somewhere? If so, can you share the source?
Once I have more information, I can better assist you in identifying the specific retractor you're interested in.