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A sinus is a sac or cavity in any organ or tissue, or an abnormal cavity or passage. In common usage, "sinus" usually refers to the paranasal sinuses, which are air cavities in the cranial bones, especially those near the nose and connecting to it. Most individuals have four paired cavities located in the cranial bone or skull.
The maxillary sinuses, the largest of the paranasal sinuses, are under the eyes, in the maxillary bones (open in the back of the semilunar hiatus of the nose). They are innervated by the maxillary nerve (CN V2). [2] The frontal sinuses, superior to the eyes, in the frontal bone, which forms the hard part of the forehead.
Frontal sinus. Each frontal sinus is situated between the external and internal plates of the frontal bone. [1] [2] Their average measurements are as follows: height 28 mm, breadth 24 mm, depth 20 mm, creating a space of 6-7 ml. [3]
The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. [1] Unlike the other three pairs of paranasal sinuses which consist of one or two large cavities, the ethmoidal sinuses entail a number of small air-filled cavities ("air cells"). [ 2 ]
In primitive bony fish and tetrapods, the nasal bones are the most anterior of a set of four paired bones forming the roof of the skull, being followed in sequence by the frontals, the parietals, and the postparietals. Their form in living species is highly variable, depending on the shape of the head, but they generally form the roof of the ...
Extension into the maxillary alveolar process may cause the roots of the molars and even premolars to lie just beneath the floor of the sinus or even project through the floor and into the sinus; in such cases, the roots of the teeth are typically surrounded by a thin layer of bone, but may sometimes lie directly underneath the mucous membrane ...
The cavity also extends into neighbouring skull bones, forming additional air cavities known as paranasal sinuses. [9] In cetaceans, the nose has been reduced to one or two blowholes, which are the nostrils that have migrated to the top of the head. This adaptation gave cetaceans a more streamlined body shape and the ability to breathe while ...
Sinus (anatomy), a sac or cavity in any organ or tissue Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including: Maxillary sinus, is the largest of the paranasal sinuses, under the eyes, in the maxillary bones; Frontal sinus, superior to the eyes, in the frontal bone, which forms the hard part of the forehead