EYE (Bulbus oculi):
• 3 tunics — fibrous (sclera + cornea), vascular (uvea: choroid + ciliary body + iris), nervous (retina).
• Lens, vitreous + aqueous humour.
• Tapetum lucidum — reflective choroidal specialization in many domestic mammals; absent in pigs and birds as well as humans.
• Eyelids (upper, lower, third) + lacrimal apparatus + extra-ocular muscles (CN III, IV, VI).

EAR:
• External ear — pinna + auditory canal + tympanic membrane.
• Middle ear — air-filled tympanic cavity, 3 ossicles (malleus, incus, stapes), Eustachian tube.
• Internal ear — bony + membranous labyrinth: cochlea (hearing) + vestibule + 3 semicircular canals (balance).
• Innervation: CN VIII (vestibulocochlear).

EYE & EAR

I. EYE — THREE TUNICS:

1. Fibrous Tunic (outer):
• Sclera — opaque white, posterior 5/6.
• Cornea — transparent, anterior 1/6; main refractive surface.
• Limbus = junction between sclera and cornea.

2. Vascular Tunic (Uvea, middle):
• Choroid — pigmented, vascular layer. In species with a tapetum lucidum, the dorsal fundus is reflective; the tapetum is fibrous in many herbivores and cellular in carnivores. It is absent in pigs and birds.
• Ciliary body — produces aqueous humour; ciliary muscle controls lens shape (accommodation).
• Iris — pigmented diaphragm; central pupil. Sphincter pupillae (CN III/parasympathetic) = constricts; dilator pupillae (sympathetic) = dilates.

3. Nervous Tunic (Retina):
• Photoreceptors: Rods (low light, night vision) + Cones (colour, daylight; very few in cattle, more in primates).
• Bipolar cells → ganglion cells → optic nerve (CN II) → optic chiasma → optic tract → lateral geniculate → visual cortex.
• Optic disc (blind spot) = where optic nerve exits; no photoreceptors.

OTHER EYE STRUCTURES:
• Lens — transparent biconvex; held by zonular fibres of ciliary body.
• Aqueous humour (anterior + posterior chambers) — produced by ciliary body, drained at iridocorneal angle.
• Vitreous body — gel filling the space between lens and retina.
• Eyelids — upper, lower, and a third eyelid (nictitating membrane) at medial canthus.
• Lacrimal apparatus — lacrimal gland (above eye) → tears → lacrimal puncta (medial canthus) → nasolacrimal duct → nasal cavity.
• Extraocular muscles — 4 recti (dorsal, ventral, medial, lateral), 2 obliques and retractor bulbi. The retractor bulbi occurs in many non-primate mammals and retracts the globe.
Innervation: CN III (oculomotor — most), CN IV (trochlear — dorsal oblique only), CN VI (abducens — lateral rectus + retractor bulbi).

II. EAR — THREE PARTS:

1. External Ear (Auris externa):
• Pinna (auricle) — funnel; supported by auricular cartilage. Erect/floppy/movable depending on species.
• External auditory canal — vertical part + horizontal part in dogs.
• Tympanic membrane (eardrum) — thin oval membrane separating outer from middle ear.

2. Middle Ear (Auris media):
• Air-filled tympanic cavity in petrous temporal bone.
• Three auditory ossicles (malleus, incus, stapes) form a chain transmitting vibrations from tympanic membrane to oval window.
• Eustachian (auditory) tube — connects middle ear to nasopharynx; equalises pressure. Diverticulum of this tube = guttural pouch in horse.
• Tympanic bulla — bony enclosure of middle ear.

3. Internal Ear (Auris interna):
• Bony labyrinth (in petrous temporal) + Membranous labyrinth (inside).
• Cochlea — spiral, snail-shaped; contains organ of Corti (hearing receptor).
• Vestibule — central chamber; contains utricle + saccule (linear acceleration + gravity sensors).
• 3 Semicircular canals (perpendicular planes) — angular acceleration / rotation sensors.
• Innervation: CN VIII (Vestibulocochlear) — cochlear branch (hearing), vestibular branch (balance).