Final answer:
An Anastomosis is the correct term for a new connection between two previously unconnected tubes, such as blood vessels or other tubular structures, either occurring naturally or surgically created.
Step-by-step explanation:
The new connection between two previously unconnected tubes is known as an Anastomosis. This term is often used in medical contexts to describe the connection between two vessels, such as blood vessels or other tubular structures in the body. An example is the ductus arteriosus, which connects the aorta to the pulmonary artery in fetal circulation, allowing blood to bypass the lungs. Similarly, arteriovenous anastomoses refer to connections between arterioles and venules, bypassing capillary beds. The anastomosis can occur naturally, such as in the aforementioned examples, or surgically, such as when connecting different parts of the intestines or other organs.
Other terms provided in the question are not the correct answer for a new connection between tubes. A Fistula is an abnormal connection between organs or vessels that normally do not connect, an Aneurysm is an abnormal bulge in the wall of an artery, and a Thrombus is a blood clot that forms in a vessel and impedes blood flow.