Electron Microscopic Observations on the Pecten of the Nighthawk (Chordeiles minor)

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Abstract
The pecten of a nocturnally active bird, the nighthawk (Chordeiles minor) has been examined by light and electron microscopy. In this species the pecten consists of a pleated, highly vascular pigmented structure. It is situated over the optic nerve head and projects into the vitreous. Several accordion folds (4–5) are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at the base. The entire pecten is enclosed in a fine basal lamina. Within each fold are numerous capillaries, larger blood vessels which could not be differentiated as to arterioles or venules and melanocytes. The capillaries are surrounded by extremely thick basal laminae composed of several fibrillar layers. These capillaries display extremely numerous microfolds on both the luminal and abluminal borders. The cell body is extremely thin with most organelles present in a paranuclear location. Pericytes are often associated with the capillaries. The melanocytes form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten is indicative of a heavy involvement in the transport of materials.