Longitudinal section of the pecten oculi of a pigeon (HE): blood vessels and capillaries
The larger vessels have a thick endothelium and are surrounded by an adventitia. It is hard to make a difference between an arteriole and a venule. The capillaries are lined only by an endothelium of which the nuclei pile out into the lumen. The pectineal capillaries are unique because of their unusually thick basal lamina, the presence of luminal and basal microfolds and the presence of pericytes (all three visible with EM)
The pigmented cells (melanocytes) of the intervascular tissue are polymorphic cells with numerous cell processes (EM) and pigmented granules distributed in their cytoplasm. These pigmented cells provide firmness to the pecten and protect the pectineal blood vessels against UV light.