In dogs and cats, communicates freely with the nasal cavity that is usually referred to as a maxillary recess (or nasal recess). Not formed between the tables of the maxillary bone, but rather bounded by the maxilla and ethmoid. In carnivores it lies immediately rostral to the orbits, dorsal to the roots of the last three cheek teeth, and communicates with the middle meatus. In horses the maxillary sinus is large and divided into caudal and rostral sinuses, it communicated with the nasal cavity via the slit-like nasomaxillary opening. The frontal and caudal maxillary sinus in the horses communicate via the frontomaillary opening. In cows the maxillary sinus is large and communicates with the nasal cavity via a large, though dorsally places nasomaxillary opening. It communicates with the large palatine sinus and lacrimal sinus (caudally) in this species as well.