#visual_system  the sensory system for vision
  supertype:  #sensory_system__sensorysystem  the body's system of sense organs
  part:  #eye__oculu__optic__peeper  the organ of sight (`peeper' is an informal term for `eye')
     part:  #choroid_coat__choroidcoat__choroid  a highly vascular membrane in the eye between the retina and the sclera
     part:  #ciliary_body__ciliarybody  the part of the tunic of the eye between the choroid coat and the iris
     part:  #eyelid__lid  either of two folds of skin that can be moved to cover or open the eye; "his lids would stay open no longer"
        part:  #eyelash__lash__cilium  any of the short curved hairs that grow from the edges of the eyelids
        part:  #conjunctiva  a transparent membrane covering the eyeball and under surface of the eyelid
     part:  #canthus  either of the corners of the eye where the upper and lower eyelids meet
     part:  #epicanthus__epicanthic_fold  a vertical fold of skin over the nasal canthus; normal for Mongolian peoples; sometimes occurs in Down's syndrome
     part:  #nictitating_membrane__nictitatingmembrane__thirdeyelid  a protective fold of skin in the eyes of reptiles and birds and some mammals
     part:  #conjunctiva  a transparent membrane covering the eyeball and under surface of the eyelid
     part:  #eyeball  the ball-shaped capsule containing the vertebrate eye
     part:  #ocular_muscle__eye_muscle__eyemuscle  one of the small muscles of the eye that serve to rotate the eyeball
     part:  #cornea  transparent anterior portion of the outer covering of the eye; it covers the lens and iris and is continuous with the sclera
     part:  #uvea  the part of the eye that contains the iris and ciliary body and choroid
     part:  #iris  muscular diaphragm that controls the size of the pupil; it forms the colored portion of the eye
        part:  #pupil  contractile aperture in the iris of the eye
     part:  #crystalline_lens__lens  biconvex transparent body situated behind the iris in the eye; it focuses light waves on the retina
        part:  #lens_capsule  a tenuous mesoblastic membrane surrounding the lens
     part:  #central_artery_of_the_retina__arteria_centralis_retinae__arteriacentralisretinae  a branch of the ophthalmic artery; enters the eyeball with the optic nerve
     part:  #ciliary_artery__ciliaryartery__arteria_ciliaris  one of several arteries supplying the choroid coat of the eye
     part:  #lacrimal_artery__arteria_lacrimalis  an artery that originates from the ophthalmic artery and supplies the lacrimal gland and rectal eye muscles and the upper eyelid and the forehead
     part:  #lacrimal_vein__vena_lacrimalis  drains the lacrimal gland; empties into the superior ophthalmic vein
     part:  #lacrimal_apparatus  the structures that secrete and drain tears from the eye
        part:  #lacrimal_gland__lachrymal_gland__lachrymalgland__tear_gland  any of the glands in the eyes that secrete tears
        part:  #lacrimal_duct__lachrymal_duct__lachrymalduct__tear_duct  any of several small ducts that carry tears from the lacrimal glands
        part:  #lacrimal_sac__tear_sac__dacryocyst  either of the two dilated ends of the lacrimal ducts at the nasal ends of the eyes that fill with tears secreted by the lacrimal glands
     part:  #retina  the light-sensitive membrane covering the back wall of the eyeball; it is continuous with the optic nerve
        part:  #neuroepithelium  epithelium associated with special sense organs and containing sensory nerve endings
        part:  #fovea_centralis__foveacentrali__fovea  area consisting of a small depression in the retina containing cones and where vision is most acute
        part:  #parafovea  area of the retina immediately surrounding the fovea
        part:  #macula_lutea__macula__macular_area__maculararea__yellow_spot  a yellowish central area of the retina that is rich in cones
        part:  #visual_cell  one of the cells of the retina that is sensitive to light
        part:  #blind_spot__blindspot__optic_disc__opticdisc__optic_disk__opticdisk  the point where the optic nerve enters the retina; not sensitive to light
        part:  #retinal_cone__retinalcone__cone__cone_cell  visual receptor cell sensitive to color
           part:  #iodopsin  a violet photopigment in the retinal cones of the eyes of most vertebrates; plays a role in daylight vision
        part:  #retinal_rod__retinalrod__rod__rodcell  visual receptor cell sensitive to dim light
           part:  #visual_purple__rhodopsin__retinal_purple__retinalpurple  a red photopigment in the retinal rods of vertebrates; dissociates into retinene by light
     part:  #sclera__sclerotic_coat__scleroticcoat  whitish fibrous membrane (albuginea) that with the cornea forms the outer covering of the eyeball
     part:  #pupillary_sphincter__pupillarysphincter__musculus_sphincter_pupillae  a ring of smooth muscle surrounding the iris
  part:  #optic_nerve__opticnerve__nervus_opticus__second_cranial_nerve__optic_tract__optictract  serves the retina

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