This skill requires Medicine. It's your ability to use instruments to insert and remove objects from one's body. You'll have to watch for blood loss, any internal damage, and warning symptoms. For stitching serious wounds, you'll need this skill at a lower level. You need delicate hands and plenty of practice to be a good surgeon. Many specialize with an extended talent in one particular area of the body.
This skill was quite primitive with much lower success rates in ancient times. If you combine this skill with Animals, you'll be able to perform surgery there as well.