Leia o trecho de livro-texto a seguir.
Arteries and veins
Arteries and veins share the same basic structure: an inner tunica intima, a middle tunica media and an outer tunica adventitia. However, they differ in important ways. Arteries carry blood away from the heart under high pressure, whereas veins return blood to the heart under low pressure. The former have a thick tunica media, rich in smooth muscle and elastic fibers, which allows them to withstand and smooth out the pressure generated by each heartbeat. The latter have thinner walls and a wider lumen, and many of them, especially in the limbs, contain valves that prevent the backflow of blood.
(Adapted from an anatomy and histology textbook)
No texto, as expressões 'The former' e 'The latter' referem-se, respectivamente, a: