| zona perforata | The perforations along the tympanic lip of the spiral lamina giving passage to the cochlear nerves. Synonym: habenulae perforata, zona perforata. (05 Mar 2000) |
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| zona pupillaris | The central region of the anterior surface of the iris located between the collarette and the pupillary margin. Synonym: zona pupillaris. (05 Mar 2000) |
| zona radiata | The thickened cell membrane of the ovum in forms, such as certain amphibia, in which it appears radially striated under the light microscope; with the electron microscope the striations can be seen to be microvilli. Synonym: membrana striata, striated membrane, zona radiata. (05 Mar 2000) |
| zona reticularis | The inner zone of the adrenal cortex. This zone consists of an anastomosing network of cells which resemble those of the zona fasciculata except for the fact that they contain less lipid. The mitochondria are elongated and contain a mixture of tubular and flattened cristae. (12 Dec 1998) |
| zona serpiginosa | <virology> A reactivation of the same Herpes virus that is responsible for chicken pox. This results in a painful blistery red rash that is confined to one side of the body. The zoster rash affects one nerve distribution or dermatome. Facial rash can lead to optic nerve involvement with resultant blindness. Synonym: shingles. (06 Mar 1998) |
| zona striata | The thickened cell membrane of the ovum in forms, such as certain amphibia, in which it appears radially striated under the light microscope; with the electron microscope the striations can be seen to be microvilli. Synonym: membrana striata, striated membrane, zona radiata. (05 Mar 2000) |
| zona tecta | The inner third of the basilar membrane of the cochlear duct extending from the tympanic lip of the osseous spiral lamina to the outer pillar cell of the spiral organ (of Corti). Synonym: zona arcuata, zona tecta. (05 Mar 2000) |
| zona vasculosa | An area in the external acoustic meatus where a number of minute blood vessels enter from the mastoid bone. Synonym: spongy spot, zona vasculosa. (05 Mar 2000) |