Openings of frontal sinus

The frontal sinus (Sinus frontalis) is carved mainly in the frontal bone; it can extend in various ways according to the species to the lacrymal, zygomatic, nasal, parietal, and even in Bulls and Pigs, into the squama of the temporal and occipital bones.

It is located on the medial side of the orbit, in the frontal region, above the lateral mass of the ethmoid bone, whose perpendicular plate becomes a part of its medial wall. It is separated from the one on the opposite side by an imperforated median wall (Septum sinuum frontalium) often a bit deviated on a side or irregular. Its cavity is more or less subdivided by incompletes a variable walls (Septa sinuum frontalium).

In Dogs, Pigs and Ruminants, it is even subdivided in independant compartments, considered as distinct sinuses. It opens in the bottom of the middle meatus, either directly, or trough the ethmoidal labyrinth.

Absent in Rabbits, developed in various ways in Carnivorous, the frontal sinus is usually very extended and complicated in Ungulates.

The Equidae are an exception: their frontal sinus only communicates with the nasal cavity through the caudal maxillary sinus.

In Equidae, it joins the sinus of the dorsal nasal concha with which it broadly communicates and that is described as its rostral compartment; it is through this compartment that the communication with the maxillary sinus is done.

In Bulls, the frontal sinus reaches its greater development. In this species, it envelops nearly completely the cranial box, isolating its internal and external tables/laminae; it extends until the nuchal reverse of the head and into the occipital bone and also delegates diverticula in the cornual processes. It complicates itself much at the same time and subdivides itself by complete walls in several parts, described as distinct sinuses.