Final answer:
The pyloric sphincter is the structure that connects the stomach to the duodenum of the small intestine.
Step-by-step explanation:
The structure that connects the stomach to the duodenum of the small intestine is known as the pyloric sphincter. This ring of smooth muscle controls the emptying of the stomach contents into the duodenum. It is positioned at the pyloric canal, the narrower end of the funnel-shaped pylorus, which is connected on the wider end to the body of the stomach.