HISTOLOGICAL AND HISTOCHEMICAL STUDIES OF THE CHOROID OF THE EYE AND ITS RELATIONS TO THE PIA-ARACHNOID MATER OF THE CENTRAL NERVOUS SYSTEM AND PERINEURAL EPITHELIUM OF THE PERIPHERAL NERVOUS SYSTEM

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Abstract
A detailed histological and histochemical study of the nature of the choroid and optic nerve covering of the eye has been made. The choroid is made up of multiple layers of flat, squamous cells along with pigment cells and a rich vascular plexus. In rat and rabbit eyes the choroid has been traced up to the pia-arachnoid directly covering the optic nerve. In the human and monkey''s eye the rich scleral tissue, entering the optic nerve through choroid-leptomeningeal junction (membranes) interferes with such serial isolation. The choroid, as well as the pia-arachnoid mater shows identical histochemical activity for various oxidative and phosphorylating groups of enzymes already tested. Because of its enzyme activity, the choroid probably acts as a metabolically active diffusion barrier isolating the sensitive retina from the surrounding body fluids, in the same way as does the perineural epithelium in peripheral nerves. The identical nature of the choroidal flat squamous cells, the perineural epithelium of the peripheral nerve fasciculus, the flat squamous cells of the pia-arachnoid mater, those covering the ciliary muscles, the endothelial-like cells of the trabecular meshwork, the flat nonpigmented cells of the iris, the capsule cells of the muscle spindle, and the lamellae of Pacinian Corpuscle is stressed. Histologi-cally, cytologically and histochemically all these structures are identical, serving the same function in different tissues of the body, although described under different names.