In anatomical sources, the aorta is usually divided into sections. One way of classifying a part of the aorta is by anatomical compartment, where the thoracic aorta (or thoracic portion of the aorta) runs from the heart to the diaphragm. The aorta then continues downward as the abdominal aorta (or abdominal portion of the aorta) diaphragm to the aortic bifurcation.
You can perform an allergy skin test on infants as young as six months, but they're not considered totally reliable in kids younger than two years old. Before going ahead with any type of skin test, a doctor usually takes a few factors into account.
I am aware it is a very new treatment that has no long term studies. We do plan to have her allergy tested in 4 months when she is 1 year old, hopefully lessening the need for any drugs. This isn't a question about my dog in particular, as we are working with my regular vet to manage her care.