The visual apparatus consists of nervous tissues immediately concerned in giving rise to sensations, supported, protected, and nourished by other parts. Its essential parts are, (1) the retina, a thin membrane lying in the eyeball and containing microscopic elements which are so acted upon by light as to stimulate (2) the optic nerve; this nerve ends (3) in a part of the brain (visual centre) which when stimulated arouses in our consciousness a feeling or sensation of sight. The visual centre may be excited in very many ways, and quite independently of the optic nerve or the retina; as is frequently seen in delirious persons, in whom inflammation or congestion of the brain excites directly the visual centre and gives rise to visual hallucinations [Newell Martin, 1895: http://bookdome.com/health/anatomy/Human-Body/The-Human-Visual-Apparatus.html].
Hierarchy: 2
Parent: peripheral nervous system
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