Browsing by Subject "Pecten oculi"

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    Electron microscopic observations on the pecten of the great blue heron (Ardea Herodias)
    (Murcia : F. Hernández, 1991) Braekevelt, Charlie R.
    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 basa1 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.
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    Fine structure of the pecten oculi in the Austral ian Gala h (Eolophus roseicapillus) (Aves)
    (Murcia : F. Hernández, 1996) Braekevelt, Charlie R.; Richardson, K.C.
    The pecten oculi of the Australian galah (Eolophus r.oseicapillus) has been examined by both light and electron microscopy. In this species the pecten is large relative to the size of the eye and is of the pleated type. It consists of 20-25 accordion folds that are joined apically by a bridge of tissue which holds the pecten in a fan-like shape widest at its base. Within each fold are many melanocytes, numerous capillaries as well as larger supply and drainage vessels. The capillaries are extremely specialized for transport functions and display extensive microfolds on both their luminal (inner) and abluminal (outer) borders. Except for the nuclear region which also 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 capillaries. The numerous pleomorphic melanocytes which more or less surround the capillaries are also presumed to be important in structural support of the pecten. The pecten represents a supplementary retinal circulation and is comparable to the falciform process of some teleosts, the conus papillaris of reptiles, the supraretinal vessels of amphibians and some teleosts and the intraretinal vessels of mammals, al1 of which are felt to be alternative methods of bringing nutrients to the inner retina.
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    Fine structure of the pecten oculi in the great horned owl (Bubo virginianus)
    (Murcia : F. Hernández, 1993) Braekevelt, Charlie R.
    The pecten oculi of the great horned owl (Bubo virginianus) has been examined by light and electron microscopy. The pecten in this species is of the pleated type and is small in comparison to the size of the eyeball. It consists of 7-8 accordion folds which are joined apically by a pigmented bridge of tissue. Within each fold are numerous capillaries, larger supply and drainage vessels and plentiful pleomorphic melanocytes. The capillaries are extremely specialized vessels, most of which display plentiful microfolds on both their luminal and abluminal surfaces although some capillaries shoW but a few microfolds. The endothblial cell bodies are extremely thin with most organelles located near the nucleus. Al1 capillaries are surrounded by a thick fibrillar basal lamina which is felt to be structurally important. Pericytes are a comrnon feature within these thickened basal laminae. The numerous melanocytes form an incomplete sheath around the capillaries and are also presumed to be fulfilling a structural role. While the morphology of the pecten in the great horned owl is certainly indicative of a heavy involvement in transport, when compared to the pecten in species that are more visually oriented it is smaller, displays fewer folds and a reduced number of microfolds within the capillaries.