Sinuses are paired air cavities/spaces (pockets) found in the cranial (head) bones. Sinuses are also referred to as "paranasal sinuses". They are connected to the nose on the facial part of the skull where air passes and mucus drains.
There are a total of four pairs of sinus cavities. They are given their names in accordance to where they are located on the face. The sinuses are the ethmoid sinuses, frontal sinuses, maxillary sinuses, and sphenoid sinuses. Everyone is born with ethmoid and maxillary sinuses and they grow as we grow. The frontal sinuses develop around the age of seven. The sphenoid sinuses develop during adolescence.
Sinuses have many responsibilities such as removing particles that we may breathe in. In addition, they filter the air and moisten it as well. They also contribute to the way our voices sound.
A healthily developed person has four pairs sinus cavities:
Between the eyes: these ones are called the ethmoid sinuses and they are located behind the bridge of the nose between the eyes. We are born with them, and as our bodies grow bigger so do they.
Forehead: the ones located above the eyes around the forehead are called the frontal sinuses, and they develop at about seven years of age.
Cheekbones: the maxillary sinuses are on either side of your nostrils in the cheek bones, and like the ethmoid sinuses we are also born with them.
Behind the eyes: the final pair of sinus cavities are deep in the skill behind the ethmoid insures and the eyes. These ones don't develop until your teenage years.
Sinus is the name for any cavity in the bodies of animals including humans. The term is generally is used in common language for the hollow air filled cavities in front of human skull.
Humans have four pairs of sinuses. That make total eight sinuses. All of these four pairs of sinuses are connected to the nasal cavity and therefore are called paranasal sinuses. Presence of these eight sinuses help to make the skull lighter and to hold up the head. They also cushion the front part of the brain.
Each of the pair of sinuses is named after a bone in skull near which the sinuses are located. Thus sinus located in the forehead just above the eyes is called frontal sinuses. Sinus located in the cheekbones on each side, which are the largest of paranasal sinuses are called maxillary sinuses. The sinuses located just above the nasal cavity are called ethmoid sinuses, and those located behind them are called sphenoid sinuses.