Sinus

The term of sinus (a “channel” or “hollow space”) is defined as any cavity within a bone but is most often used to identify the muscus lined air cavities in the facial bones and certain blood passageways in animals. In humans, sinuses surround the nose and are known as the paranasal sinuses. They extend from the nasal cavities into adjoining bones and are connected to the nose by passageways. The panasal sinuses are thought to help warm and moisten inhaled air. They also reduce the weight of the skull and perhaps modify vocal sounds. The bones that contain sinuses are the frontal, sphenoid, ethmoid, and maxillary bones.

The paranasal sinuses are lined with a mucosa, or moist membrane. Glands are present within the mucosa, and ciliated and gobiet cells occurs on the surface, exposed to the air space in the sinus. The ciliated cells exhibit hairlike processes that beat back and forth. They serve to keep the air that enters the lungs clean by trapping dust and dirt. The particles and mucus eventually reach the pharynx and are swallowed. An inflammation of the mucosa is called sinusitis.

Sinuses in blood passageways include the capillary spaces of the liver; spaces in the common carotid artery and the aorta; and maternal sinusoids, which are small channels in the wall of the uterus of a pregnant woman.

The Hyoid Bone

The Hyoid bone is named from its resemblance to the Greek upsilon; it is also called the lingual bone, because it supports the tongue and gives attachment to its numerous muscles. It is a bony arch, shaped like a horseshoe, and consisting of five segments, a body, two greater cornua, and two lesser cornua. It is suspended from the tip of the styloid processes of the temporal bone by ligmentous bonds, the style hyoid ligaments.

The body (basi hyal) forms the central part of the bone, and is of a quadric-lateral form; its anterior surface, convex, directed forward and upward, and is crossed at right angles by a horizontal ridge, so that this surface is divided into four spaces or depressions. At the point of meeting of these two lines is a prominent elevation, the tuberele. The portion above the horizontal ridge is directed upward, and is sometimes described as the superior border. The anterior surface gives attachment to the Genio-hyoid in the greater part of its extent; above, to the Genio-hyo-glossus; below, to the Mylo-hyoid, Styly-hyoid, and sponeurosis of the Digastric (suprahyoid spontaneurosis); and between these to part of the Hyo-glossus. The posterior surface is smooth, concave, directed backward and downward, and separated from the epiglottis by the thyro-hyoid membrane and by a quantity of loose areolar tissue. The superior border is rounded, and gives attachment to the thyroid membrane, part of the Genio-hyo-glossi and Chondro-glossi muscles. The inferior border gives attachment, in front, to the Sterno-hyoid; behind, to the Omo hyoid and to part of the Thyro-hyoid at its junetion with the great cornu. It also gives attachment to the Lavatore glandule thyroidere when this muscle is present. The lateral surfaces after middle life are joined to the greater cornua. In early life they are connected to the cornua by eartilaginous surfaces, and held together by ligaments, and occasionally a synovial membrane is found between them.

Ear

The ear is the organ of hearing and equilibrium (balance) in vertebrates. The ear converts sound waves in the air to nerve impulses that are relayed to the brain, where they are interpreted as sound rather than as mere vibrations. The innermost portion of the ear maintains Biological Equilibrium through the so-called vestibular apparatus, which includes the semicircular canals. Any change in the position of the head or body causes the apparatus to transmit nerve impulses to the brain, evoking muscular apparatus is basically alike in all vertebrates; hearing structures evolved later in the higher vertebrates.

Many vertebrates also have specialized sense organs, rather than ears, for hearing and equilibrium. Crickets and spiders, for example, have membranes much like sounding boards on the legs. Moths have a similar rudimentary ear on the thorax that apparently serves as a warning system for attacks by bats.

Structure of the Ear
The ear in humans and most other mammals consist of three parts; the outer, middle, and inner portions. The outer ear, or pinna, is the structure commonly called the ear. It is a skin covered flap of elastic cartilage projecting from the side of the head and funneling sound into the middle ear. The middle ear is an air filled chamber containing the eardrum, or tympanic membrane, and connected to the pharynx by the Eustachian tube, thus equalizing the pressure on the two sides of the eardrum. The inner ear contains the sensory receptors for hearing; these receptors are in a fluid filled chamber called the cochlea. The middle and outer ears serve only to receive and amplify sound waves and occurs only in amphibians and mammals, whereas the inner ear is present in all vertebrates.

In fish, the inner ear is primarily an organ of equilibrium and lacks a cochlea; nor do fish have outer or middle ears. Amphibians posses a middle ear cavity; a thin membrane separating the middle ear from the outside becomes the eardrum. The pinna occurs only in mammals. In birds and reptiles, the eardrum may be in a depression below the surface of the head.