Pre-papillary cyst developed from remnants of the hyaloid artery.

THE duct of Cloquet is a tubular area which traverses the eyeball in its anterior-posterior axis from the optic disk to the posterior pole of the lens. It develops at the expense of the central or original vitreous, which is progressively absorbed from the third month of intra-uterine life, during the formation of the definitive vitreous. In the human fqetus the duct of Cloquet exists from the sixth month and generally disappears shortly after birth. It contains the hyaloid artery, the ramifications of which form a vascular sheath embracing the posterior lens capsule. In young children, and even in adults, remnants either of the duct of Cloquet or of the hyaloid artery can sometimes be seen. The duct of Cloquet may persist in the shape of a membrane, which is inserted into some part of the optic disk, covers the emergence of the vessels and ends in the vitreous, either in the form of a point or club, or in the form of membranous expansions. Some types of hyaloid remnants are easily recognized. The following are some examples: (1) A white tubercle, bright and quite small found on the emergence of the central retinal artery like a bud on the bough of a fruit-tree. (2) An arterial handle leaving the optic disk and projecting into the vitreous. (3) A mobile cord or dark'filament, arising from the optic disk and ending by a free extremity in the vitreous. These prepapillary formations should not be mistaken for hyaline drusen at the optic disk or for the epipapillary membrane. The latter covers the whole of the optic disk and is attached to the vessels where they emerge. It may be opaque or transparent and somewhat ill-defined, and may encroach slightly upon the neighbouring retina. Very exceptionally one can find prepapillary cystic formations, probably related to remnants of the hyaloid artery. The cases of Durst (1909), Risley (1896), Koller (1900), Paton (1910), Levitt and Lloyd (1939), Yudkin (1926), Hilgartner (1940), Levine (1932), Purtscher (1936) and Merigot de Treigny and Subileau (1927) are