Electron microscopic observations on the pecten of the great blue heron (Ardea herodias).

The pecten oculi of the great blue heron (Ardea herodias) has been examined by both light and electron microscopy. In this species the pecten is large and of the pleated type. It consists of 14-15 acordion folds that are joined apically by a more heavily pigmented bridge of tissue which holds the pecten in a fan-like shape widest at its base. As in other species it is situated over the optic nerve head and projects out into the vitreous. Within each fold are numerous capillaries, larger supply and drainage vessels and many melanocytes. The capillaries are extremely specialized vessels which display extensive microfolds on both their luminal and abluminal borders. The endothelial cell bodies are extremely thin with most organelles present in a paranuclear location. The capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally useful. Pericytes are a common feature of these capillaries. The numerous pleomorphic melanocytes which form an incomplete sheath around the capillaries and other blood vessels are also felt to be important in structural support of the pecten. The morphology of the pecten of the great blue heron is indicative of a heavy involvement in the transport of materials.