Venule
A little vein.
Venules go from capillaries to veins, vessels that carry blood low in oxygen content from the body back to the heart.
The deoxygenated form of hemoglobin (deoxyhemoglobin) makes the blood in veins and venules appear dark.
Veins and venules are part of the afferent wing of the circulatory system which returns blood to the heart.