What kind of stitch is taken and tied separately and used for reinforcemement of a primary suture line?

The stitch you are referring to is known as a "purse-string suture." This technique involves taking a continuous stitch around the edge of the tissue and then tightening it to gather the tissue together, providing reinforcement to the primary suture line. Purse-string sutures are commonly used in various surgical procedures, especially for closing or reinforcing hollow organs. They help to minimize tension on the primary suture line and promote better healing.