Final answer:
The midgut's first rotation happens around the axis of the superior mesenteric artery, a major branch of the abdominal aorta that supplies blood to parts of the small and large intestines and the pancreas.
Step-by-step explanation:
The midgut's first rotation occurs around the axis of the superior mesenteric artery. This artery arises from the abdominal aorta and is one of its major branches. It is responsible for supplying blood to a significant portion of the small intestine (duodenum, jejunum, and ileum), as well as parts of the large intestine, and the pancreas. The process of embryological rotation of the midgut is critical for the proper positioning of the intestines within the abdominal cavity.