Fine structure of the conus papillaris in the bobtail goanna (Tiliqua rugosa)

Abstract

The structure of the conus papillaris in an Australian lizard. the bobtail goanna (Tiliqua rugosa) was investigated by lipht and electron microscopy. In this strongly diurrial species, the conus papillaris consists of a heavily vascularized and pigmented, finger-like structure about 1 mm ir1 diameter and 3-3 mm in length. It is situated over the optic nerve head and projects into the vitreous chamber. Within the conus are numerous capillaries and larger blood vessels. melanocytes and occasional mast cells. Many of the capillaries display prominent luminal and abluminal microfolds. Other capillaries show no microfolds while still others display an intermediate number of microfolds. The larger blood vessels are usually indistinguishable as to being either arterioles or venules. The endothelial cells of al1 blood vessels show a population of cytoplasmic granules. The melanocytes are large pleomorphic cells usually rich in microfilaments. Unmyelinated nerve processes are plentiful within the conus and the Schwann cells ericlosing these nerve fibres are occasionally seen to be pigmented. The rnorphology of the conus papillaris indicates a heavy involvernent in the transport of materials. It is considered to be homologous to the pecten oculi of the avian eye: to the falciform process of the teleost eye; to the supraretinal vessels of amphibians and to the intraretinal vessels of the mammalian eye.