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1. a covering structure or layer of cells.
2. a stratum in the human brain composed of fibers from the body and splenium of the corpus callosum sweeping around the lateral ventricle.
tapetum lu´cidum the iridescent epithelium of the choroid of animals that gives their eyes the property of shining in the dark.
A layer of tissue in the choroid of the eye between the vascular and capillary layers in some animals, but not in humans. This membrane reflects light shined into the animal's eyes. It produces a green reflection, readily seen in cats.Synonym: tapetum choroideae
See also: tapetum
A reflecting pigment layer lying behind the visual receptors of the retina of certain mammals (e.g. cats, dogs), birds and fish, which gives a shining appearance to the eyes when illuminated in the dark. The tapetum is located either in the pigment epithelium or in the choroid and covers either the whole fundus or more often only the upper and back portion. The role of the tapetum lucidum is to increase the probability of visual stimulation of the photoreceptors by reflecting light back after having already traversed them once, thus aiding vision in dim illumination. In some species the tapetum consists of guanine crystals.