Perpendicular plate

The perpendicular plate is in general more extended that the horizontal one; it contributes to delimitate laterally the guttural opening of the nasal cavity or choane. Flattened from one side to the other, it presents two surfaces and four borders.

The nasal surface (Facies nasalis) is concave and smooth, except in its caudal part, that is rough to receive the pterygoid bone.

The maxillar surface (Facies maxillaris), lateral, is irregular. Its rostral part, rough, unites to the maxilla; it is travelled by a deep groove that contributes to form the great palatine duct (Canalis palatinus major). Its middle part, smooth and excavated, contributes to form the pterygopalatine fossa (Fossa pterygopalatina), at the bottom of which stands the caudal orifice of the foramen palatin caudal (Foramen palatinum caudale). The caudal part, rough, unites to the pterygoid process of the spenoid bone.

The rostral border is oblique upwards and backwards; it is united to the maxilla and the ethmoid bone. It forms, dorsally to the caudal orifice of the great palatine duct, the sphenopalatine foramen (Foramen sphenopalatinum), formerly 'nasal hole'. A bit more dorsally, this border detach on the medial border a crest that continues more or less on the nasal surface and until the sphenoid; this crest enters ventrally in contact with the vomer and unites rostro-dorsally to the basal plate of the ethmoid bone: it is the sphenoethmoidal plate (Lamina sphenoethmoidalis), particularly long in dogs and pigs but not very distinct in other species, that contributes to separate the naso-pahryngeal meatus of the ethmoidal labyrinth.

The caudal border, oblique as the previous one, is first free, then unites caudally to the pterygoid process of the sphenoid bone; in Ungulates and Carnivorous, it contributes to form a long crest with it, called pterygo-palatine; it is covered on the medial side by the pterygoid bone. Its free part holds the pyramidal process (Processus pyramidalis) that enclaves itself before the pterygoid fossa. This process forms an acuminate (pointy-ended) relief in Men, a thick and prominent tuberosity in Pigs, a poured-out plate in Equidae, reduced to a simple roughness in Ruminants, it is absent in Carnivorous.

The ventral border goes on with the horizontal plate; it is separated from the maxillar tuberosity by a longitudinal vasculo-nervous groove, generally narrow, that could be called caudal palatine sinus (formerly 'staphyline fissure')

The dorsal border is divided into two prolongations: one, lateral, goes in direction of the frontal bone inside the orbital wall: it is the orbital process (Processus orbitalis). The other goes medially, under the body of the sphenoid bone, it is the sphenoidal process (Processus sphenoidalis). These extensions, very developed in men, are weaker if any in domestic species. In Equidae and at a lesser degree in Pigs, the perpendicular plate of the palatine bone is carved by a dependance of the spheoidal sinus (Sinus sphenoidalis).