Fine structure of the pecten oculi of the emu (Dromaius novaehollandiae).

The pecten oculi of the emu (Dromaius novaehollandiae) has been examined by light and electron microscopy. In this species the pecten is small relative to the size of the globe and is of a primitive pleated type. It consists of only 3-4 loose folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Each fold is quite thick (100-120 microns) and has a central core of mostly unpigmented cell processes. In this central region are supply or drainage vessels while numerous melanocytes and pecteneal capillaries are only located at the periphery of the folds. The capillaries are extremely specialized for transport functions and for the most part display extensive microfolds on both their luminal (inner) and abluminal (outer) borders although capillaries with very few microfolds are also noted. An unusual feature of some capillaries is luminal folds of the cell body with further luminal microfolds superimposed on them. Except for the nuclear region which contains most of the organelles, the endothelial cell bodies are extremely thin. These capillaries are surrounded by thick fibrillar basal laminae which are felt to be structurally important. Pericytes are a common feature within the basal lamina of these capillaries. The numerous peripherally located melanocytes which more or less surround the capillaries are also presumed to be important for structural support of the pecten. The large number of cell processes forming the central core of each fold are felt to be unpigmented processes of the melanocytes.