The kind of blood vessels which doesn't have no muscular walls is veins. Veins are actually any of the tubes forming part of the blood circulation system of the body, carrying mainly oxygen-depleted blood towards the heart. They usually carry deoxygenated blood from our body to the heat (except pulmonary artery) Veins are less muscular than arteries and are often closer to the skin. There are valves in most veins to prevent backflow.

Most veins are equipped with valves to prevent blood flowing in the reverse direction.

Veins are translucent, so the color a vein appears from an organism's exterior is determined in large part by the color of venous blood, which is usually dark red as a result of its low oxygen content. Veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the highly energetic blue wavelengths to penetrate through to the dark vein and reflect back to the viewer. The colour of a vein can be affected by the characteristics of a persons skin, how much oxygen is being carried in the blood, and how big and deep the vessels are.When a vein is drained of blood and removed from an organism it appears grey-white

Veins are the kind of blood vessels which have no muscular walls..