The optic cup is connected to the brain by the optic stalk, which has a groove, the choroid fissure, on its ventral surface (Figs. 17.2 and 17.3). In this groove are the hyaloid vessels. The nerve fibers of the retina returning to the brain lie among cells of the inner wall of the stalk (Fig. 17.8). During the seventh week, the choroid fissure closes, and a narrow tunnel forms inside the optic stalk (Fig. 17.8B). As a result of the continuously increasing number of nerve fibers, the inner wall of the stalk grows, and the inside and outside walls of the stalk fuse (Fig. 17.8C). Cells of the inner layer provide a network of neuroglia that support the optic nerve fibers.
The optic stalk is thus transformed into the optic nerve. Its center contains a portion of the hyaloid artery, later called the central artery of the retina. On the outside, a continuation of the choroid and sclera, the pia arachnoid and dura layer of the nerve, respectively, surround the optic nerve.
Outer layer of optic stalk
Lumen of optic stalk
Nerve fibers Hyaloid artery Choroid fissure
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