Figure 13.3a The eye and accessory structures. Eyebrow Eyelid Eyelashes Site where conjunctiva merges with cornea Palpebral fissure Lateral commissure Iris Eyelid Pupil Sclera (covered by conjunctiva) Lacrimal caruncle Medial commissure Surface anatomy of the right eye © 2014 Pearson Education, Inc.

Figure 13.4 The lacrimal apparatus. Lacrimal sac Lacrimal gland Excretory ducts of lacrimal glands Lacrimal punctum Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril © 2014 Pearson Education, Inc.

Figure 13.5 Extrinsic eye muscles. Trochlea Superior oblique muscle Superior oblique tendon Superior rectus muscle Axis of rotation of eye Lateral rectus muscle Inferior rectus muscle Medial rectus muscle Lateral rectus muscle Common tendinous ring Inferior rectus muscle Inferior oblique muscle Lateral view of the right eye Superior view of the right eye Muscle Action Controlling cranial nerve Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique Moves eye laterally Moves eye medially Elevates eye and turns it medially Depresses eye and turns it medially Elevates eye and turns it laterally Depresses eye and turns it laterally VI (abducens) III (oculomotor) IV (trochlear) © 2014 Pearson Education, Inc. Summary of muscle actions and innervating cranial nerves

Figure 13.6a Internal structure of the eye (sagittal section). Ora serrata Ciliary body Sclera Ciliary zonule (suspensory ligament) Choroid Retina Macula lutea Cornea Fovea centralis Iris Pupil Posterior pole Optic nerve Anterior pole Anterior segment (contains aqueous humor) Lens Central artery and vein of the retina Scleral venous sinus Posterior segment (contains vitreous humor) Optic disc (blind spot) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. © 2014 Pearson Education, Inc.

Figure 13.13c Focusing for distant and close vision. View Ciliary muscle Lens Ciliary zonule (suspensory ligament) The ciliary muscle and ciliary zonule are arranged sphincterlike around the lens. As a result, contraction loosens the ciliary zonule fibers and relaxation tightens them. © 2014 Pearson Education, Inc.

Figure 13.7 Pupil constriction and dilation, anterior view. Parasympathetic + Sympathetic + Sphincter pupillae muscle contracts: Pupil size decreases. Iris (two muscles) • Sphincter pupillae • Dilator pupillae Dilator pupillae muscle contracts: Pupil size increases. © 2014 Pearson Education, Inc.

Figure 13.8 Microscopic anatomy of the retina. Neural layer of retina Pigmented layer of retina Pathway of light Choroid Sclera Optic disc Central artery and vein of retina Optic nerve Posterior aspect of the eyeball Ganglion cells Bipolar cells Photoreceptors Choroid • Rod Outer segments of rods and cones Axons of ganglion cells • Cone Nuclei of ganglion cells Amacrine cell Horizontal cell Pathway of signal output Nuclei of bipolar cells Nuclei of rods and cones Pigmented layer of retina Axons of ganglion cells Pigmented layer of retina Pathway of light © 2014 Pearson Education, Inc. Cells of the neural layer of the retina Photomicrograph of retina

Light absorption (percent of maximum) Figure 13.11 The electromagnetic spectrum and photoreceptor sensitivities. (109 nm =) 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m 103 m Gamma rays X rays UV Infrared Micro- waves Radio waves Visible light Blue cones (420 nm) Green cones (530 nm) Red cones (560 nm) Rods (500 nm) 100 Light absorption (percent of maximum) 50 400 450 500 550 600 650 700 Wavelength (nm) © 2014 Pearson Education, Inc.

Figure 13.10 Circulation of aqueous humor. Posterior segment (contains vitreous humor) Iris Cornea Lens Lens epithelium Lens Cornea 2 Corneal epithelium Corneal endothelium Aqueous humor Aqueous humor forms by filtration from the capillaries in the ciliary processes. 1 Anterior chamber Anterior segment (contains aqueous humor) Ciliary zonule (suspensory ligament) Posterior chamber Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor (not shown). 2 3 Scleral venous sinus 1 Ciliary processes Corneoscleral junction Ciliary body Ciliary muscle Bulbar conjunctiva Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus. 3 Sclera © 2014 Pearson Education, Inc.

Figure 13.13 Focusing for distant and close vision. Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image Lens flattens for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Parasympathetic activation Divergent rays from close object Inverted image Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. View Ciliary muscle Lens Ciliary zonule (suspensory ligament) The ciliary muscle and ciliary zonule are arranged sphincterlike around the lens. As a result, contraction loosens the ciliary zonule fibers and relaxation tightens them. © 2014 Pearson Education, Inc.

© 2014 Pearson Education, Inc. Figure 13.18 Visual pathway to the brain and visual fields, inferior view. Both eyes Fixation point Right eye only Left eye only Right eye Left eye Optic nerve Supra- chiasmatic nucleus Pretectal nucleus Optic chiasma Optic tract Lateral geniculate nucleus Superior colliculus (sectioned) Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber Lateral geniculate nucleus of thalamus Optic radiation Superior colliculus Occipital lobe (primary visual cortex) Corpus callosum The visual fields of the two eyes overlap considerably. Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma. Photograph of human brain, with the right side dissected to reveal internal structures. © 2014 Pearson Education, Inc.

Figure 13.21a Structure of the ear. Middle ear Internal ear (labyrinth) External ear Auricle (pinna) Helix Lobule External acoustic meatus Tympanic membrane Pharyngotympanic (auditory) tube The three regions of the ear © 2014 Pearson Education, Inc.

Route of sound waves through the ear Figure 13.25a Pathway of sound waves and resonance of the basilar membrane. Auditory ossicles Malleus Incus Stapes Cochlear nerve Scala vestibuli Oval window Helicotrema 4a Scala tympani Cochlear duct 2 3 Basilar membrane 4b 1 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Tympanic membrane Round window Route of sound waves through the ear Sound waves vibrate the tympanic membrane. 1 Auditory ossicles vibrate. Pressure is amplified. 2 Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. 3 4b Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. © 2014 Pearson Education, Inc.

Figure 13.26 Structure of a macula. Macula of utricle Macula of saccule Kinocilium Otolith membrane Otoliths Stereocilia Hair bundle Hair cells Supporting cells Vestibular nerve fibers © 2014 Pearson Education, Inc.