When Froriep said, "Like Athena from the brow of Zeus springs the vertebrate eye into existence," he expressed the near despair which has been felt by many students of the problem of the origin of the vertebrate eye. The comparative anatomy of this intricate organ affords few clues to the history of the parts of the eyeball previous to their present association. The eye of the fish is as complex as that of man, and the structural variations of eyes are largely expressions of habit differences rather than stages in a majestic phylogenetic progress of increasing complexity and perfection, such as one sees in the heart, the brain, the ear or indeed in almost any other organ.
It is a commonplace to say of the retina that it is in reality a portion of the brain wall. The homologizations of the sclera and uvea with the dura and pia-arachnoid, respectively,
WALLS GL. ORIGIN OF THE VERTEBRATE EYE. Arch Ophthalmol. 1939;22(3):452–486. doi:10.1001/archopht.1939.00860090118018
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