. The development of the chick; an introduction to embryology . )tic stalk; but on the fifth daythe formation of fibers begins from more distal portions of theretina and these do not grow towards the insertion of the opticstalk, l)ut towards the choroid fissure; arrived there, they l)endcentrally and run in a bundle on each side along the floor of thebulbus oculi to the optic stalk, where they join with the fillers firstformed. The later formed fillers pass to still more distal portions. FiG. 164. — Section in the plane of d of Fig. 162, toshow the histological structure. (After Bernd.)Alibrev
. The development of the chick; an introduction to embryology . )tic stalk; but on the fifth daythe formation of fibers begins from more distal portions of theretina and these do not grow towards the insertion of the opticstalk, l)ut towards the choroid fissure; arrived there, they l)endcentrally and run in a bundle on each side along the floor of thebulbus oculi to the optic stalk, where they join with the fillers firstformed. The later formed fillers pass to still more distal portions. FiG. 164. — Section in the plane of d of Fig. 162, toshow the histological structure. (After Bernd.)Alibreviations as Ixfore. of the choroid fissure, and, as the pecten forms in the manneralready described, the fibers of the optic nerve all unite l)eneathit on their way to the original optic stalk. Thus, the optic nerveobtains an insertion coincid(Mit in length with the base of thepecten, and its filwrs, racUating off into the retina on each sideof the pecten, se})ai-ate the latter completely from the choroidcoat of the eyeball. The optic stalk is at first a tubuhir communication betweenthe optic vesicle and the fore-brain, and its walls are an epitheliallayer of the same thickness throughout. The fillers of the oi)tic ORGANS OF SPECIAL SENSE 285 nerve grow into its ventral wall exclusively, between its epithelialcells, which gradually become disarranged and irregular. Thusthe ventral wall l)ecomes increasingly thick and the lumen excen-tric. By the sixth day the lumen appears in cr
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