The narrow tube from the tip of the middle ear to the pharynx is called Eustatian tube. It keeps air pressure equal on both sides of the tympanic membrane. It is named after the 16th century Italian physician Bartolommo Eustachio.

The middle ear is located inside the tympanic bone of the crown. The parts of the middle ear are the eustachian tube, the cochlea and the sphincter.
1. Eustatian Tube: The narrow tube from the tip of the middle ear to the pharynx is called Eustatian tube. It keeps air pressure equal on both sides of the tympanic membrane. It is named after the 16th century Italian physician Bartolommo Eustachio.
2. Ear Ossicles: There are 3 small bones in the middle ear. These are-
(i) Malleus: It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus
(ii) Incus : It looks like anvil. One end is attached to the malleus and the other end to the stapes
(iii) Stepis: Stepis looks triangular or like the stirrup of a horse saddle. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.
Function: Bones conduct sound waves from the tympanic membrane to the cochlea.
3. Opening: There are two openings in the middle ear. Fenestra ovalis (oval window) at the top and fenestra rotanda (round window) at the bottom. Sound enters the cochlea through the fenestra ovalis and exits through the fenestra rotanda.

The oval and elastic membrane at the end of auditory meatus is called tympanic membrane. Its outer side is concave and inner side is convex. It separates the outer and inner ear. It has a diameter of 9 mm, thickness of 0.1 mm and weight of 14 mg. If this screen is damaged, it is not easily reconstructed. Through this the sound waves enter the middle ear.

The narrow duct from the pinna to the tympanic membrane is called the external auditory meatus. It is a curved tunnel. Its outer two-thirds is made up of cartilage and the inner one-third is made up of bone. Its length is 2.5 cm and width is 0.7 cm. It contains wax glands and fine hairs. Through this the sound waves reach the tympanic membrane. Due to wax and hair, dust and germs cannot enter inside.

The flat, flexible and skin-covered part located on both sides of the head is called pinna. It is funnel-shaped, hairy and composed of cartilage. Its length is 6-6.4 cm and width is 3 cm. It has a small and round hole. The eardrum consists of several cochlear muscles. Pinna cannot be moved because the muscles are not contractile. Because of this, to hear a sound well, the head along with the ear hole has to be turned towards the sound. Sound is transmitted to the external auditory meatus through the pinna.

The external part of the ear is called external ear. This is the first part of the ear. It consists of three parts.
1. Pinna: The flat, flexible and skin-covered part located on both sides of the head is called pinna. It is funnel-shaped, hairy and composed of cartilage. Its length is 6-6.4 cm and width is 3 cm. It has a small and round hole. The eardrum consists of several cochlear muscles. Pinna cannot be moved because the muscles are not contractile. Because of this, to hear a sound well, the head along with the ear hole has to be turned towards the sound. Sound is transmitted to the external auditory meatus through the pinna.
2. Auditory Meatus: The narrow duct from the pinna to the tympanic membrane is called the external auditory meatus. It is a curved tunnel. Its outer two-thirds is made up of cartilage and the inner one-third is made up of bone. Its length is 2.5 cm and width is 0.7 cm. It contains wax glands and fine hairs. Through this the sound waves reach the tympanic membrane. Due to wax and hair, dust and germs cannot enter inside.
3. Tympenic Membrane: The oval and elastic membrane at the end of auditory meatus is called tympanic membrane. Its outer side is concave and inner side is convex. It separates the outer and inner ear. It has a diameter of 9 mm, thickness of 0.1 mm and weight of 14 mg. If this screen is damaged, it is not easily reconstructed. Through this the sound waves enter the middle ear.

The organ through which animals maintain hearing and body balance is called ear. It is located at the Srætikotra on either side of the head. Each ear consists of three parts. Outer ear, middle ear and inner ear.
A. External: The external part of the ear is called external ear. This is the first part of the ear. It consists of three parts.
1. Pinna: The flat, flexible and skin-covered part located on both sides of the head is called pinna. It is funnel-shaped, hairy and composed of cartilage. Its length is 6-6.4 cm and width is 3 cm. It has a small and round hole. The eardrum consists of several cochlear muscles. Pinna cannot be moved because the muscles are not contractile. Because of this, to hear a sound well, the head along with the ear hole has to be turned towards the sound. Sound is transmitted to the external auditory meatus through the pinna.
2. Auditory Meatus: The narrow duct from the pinna to the tympanic membrane is called the external auditory meatus. It is a curved tunnel. Its outer two-thirds is made up of cartilage and the inner one-third is made up of bone. Its length is 2.5 cm and width is 0.7 cm. It contains wax glands and fine hairs. Through this the sound waves reach the tympanic membrane. Due to wax and hair, dust and germs cannot enter inside.
3. Tympenic Membrane: The oval and elastic membrane at the end of auditory meatus is called tympanic membrane. Its outer side is concave and inner side is convex. It separates the outer and inner ear. It has a diameter of 9 mm, thickness of 0.1 mm and weight of 14 mg. If this screen is damaged, it is not easily reconstructed. Through this the sound waves enter the middle ear.

B. Middle Ear: The middle ear is located inside the tympanic bone of the crown. The parts of the middle ear are the eustachian tube, the cochlea and the sphincter.
1. Eustatian Tube: The narrow tube from the tip of the middle ear to the pharynx is called Eustatian tube. It keeps air pressure equal on both sides of the tympanic membrane. It is named after the 16th century Italian physician Bartolommo Eustachio.
2. Ear Ossicles: There are 3 small bones in the middle ear. These are-
(i) Malleus: It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus
(ii) Incus : It looks like anvil. One end is attached to the malleus and the other end to the stapes
(iii) Stepis: Stepis looks triangular or like the stirrup of a horse saddle. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.
Function: Bones conduct sound waves from the tympanic membrane to the cochlea.
3. Opening: There are two openings in the middle ear. Fenestra ovalis (oval window) at the top and fenestra rotanda (round window) at the bottom. Sound enters the cochlea through the fenestra ovalis and exits through the fenestra rotanda.
C. Internal Ear: The inner ear is located inside the auditory capsule or shrutikotar of the crown. Its main part is the membranous labyrinth. It is covered by bony labyrinth. The membranous labyrinth is filled with endolymph and the bony labyrinth with perilymph. The inner ear consists of two chambers. The human balance organ is called the vestibular apparatus. It is composed of utriculus and sacculus.
1. Utriculus: The spherical chamber at the top of the inner ear is called utriculus. It consists of 3 semicircular canals. 2 vertical ducts and 1 horizontal duct. The ducts are located at right angles to each other. One end of each duct swells to form an ampulla.
The ampulla contains the sensory cells or macula. Sensory cells give rise to sensory hair cells. Sensory hair cells are embedded in otolith grains (stones). Otolith granules are covered by cupula. Utriculus maintains body balance.
2. Sacculus: The lower chamber of the inner ear is called sacculus. It forms a patchy tube like a snail shell. It is called cochlea. Cochlea has 3 chambers. scala vestibuli, scala media and scala tympani. The scala vestibuli is superior and filled with perilymph, the scala media is medial and filled with endolymph, and the scala tympani is inferior and filled with perilymph. The scala media consists of Ressner’s membrane above and Basil’s membrane below. Some epithelial cells above the basilar membrane transform to form the organ of Corti. Organ of Corti is a sensory organ. Organ of Corti contains 5000 sensory neurons. The place where the scala vestibula and scala tympani meet is called the helicotrima.

1. A reflection of an object is seen with both eyes.
2. Objects can be deeply understood.
3. The field of vision is much larger.
4. Different tasks can be done correctly.
5. Binocular vision can accurately assess the shape and depth of an object.
6. If there is a problem in one eye, it can be seen by the other eye.
7. Distance of objects can be sensed accurately.
8. Three-dimensional vision of objects can be observed.

When a three-dimensional image of an object is formed in two eyes of a person, it is called binocular vision.
A characteristic or condition of binocular vision
1. The object must be present in the retina of both eyes.
2. A similar image of the object will be formed on the retina of both eyes.
3. The two observatories will meet at one place.

1. Near object vision technique: During near object vision the circular muscle of the ciliary body contracts and the suspensory ligament is stretched. It increases the curvature of the lens. The lens becomes thicker and shorter and the focal length decreases. Light rays from the object fall on the retina and an image is formed.
2. Techniques for viewing distant objects: During viewing of distant objects, the circular muscle of the ciliary body stretches and the suspensory ligament contracts. It reduces the curvature of the lens. The lens becomes narrower and longer and the focal length increases. Light rays from the object fall on the retina and an image is formed.