Fine structure of the pecten of the pigeon (Columba livia).

The pecten oculi of the diurnally active pigeon (Columba livia) has been examined by light and electron microscopy. In this species the pecten is of the pleated type. It is situated over the optic nerve head and extends out into the vitreous. Fifteen to 17 accordion folds are joined apically by a heavily pigmented ridge of tissue which holds the pecten in a fan-like shape, widest at the base. The entire pecten is enclosed by a fine basal lamina. Within each fold are numerous capillaries, larger blood vessels and melanocytes. The capillaries are surrounded by thick fibrillar basal laminae which often contain pericytes. These capillaries display numerous microfolds on both the luminal and abluminal borders. The endothelial cell body is extremely thin with most organelles present in a paranuclear location. The melanocytes which are more plentiful in the bridge region form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten in the pigeon is indicative of a heavy involvement in the transport of materials.