Retinal circulation in some lower vertebrates.

Four Elasmobranchs, 23 Teleosts, 2 Holosteans, 1 Urodele and 2 Anurans were studied. In Elasmobranchs, no vessel is found either in the vitreous cavity or on the retina. The iris artery proceeds through the ventral choroid and sends off a branch to the small lens muscle papilla. Most instances in the Teleosts are classified into 4 types; the higher falciform process, the low falciform process, the low falciform process with branches on the retina, and the vitreal vessels; depending upon the development of the hyaloid artery either into the vitreous cavity along the embryonic fissure or onto the retina. The main vessel which proceeds from the optic disc to the lens muscle tends to be obliterated in the vitreal vessels where the embryonic fissure is closed and the numerous branches on the retina are received by a peripheral annular- vessel. Instances which do not fall into any of these categories are considered to be deviations. The arterial entry near the ventral ora in Holostei is associated with the ventralward elongation of the optic disc. The vitreal vessels of Liparids are unique in that their exit is through the optic disc. Urodela show an avascular condition, while Anura have a well developed system of vitreal vessels where the entry and the exit are at the ventral margin of the ventral lens muscle represented by a small swelling in the ciliary folds. In both, the ophthalmic artery runs along the ventro-temporal meridian of the eye-ball to supply the cilio-iris region. -- The falciform process type vascularization may have arisen from the vitreal vessels due to their being influenced by the development of the accommodative lens muscle, which is functional only in Neopterygii. On the other hand, both in Classes Chondrichthyes and Amphibia, it seems that the less marked lens muscle has not had any significant effect on intraocular vascularization

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