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The vomer bone is a rigid, triangular organ in the skull of most vertebrates. Part of the nasal septum, the bone is one of the singular facial bones that exists without a corresponding bone. Long, thin, and flat, it separates the nasal passages. It is also considered responsible for perceiving certain pheromones.
Lying dorsal to the hard palate, the vomer bone defines the features of the face with several other bones. These include the sphenoid, left and right palatine bones, ethmoid, and left and right maxillary bones. The ethmoid bone itself fits into the groove of the vomer. Many animals, cats in particular, have a well-defined vomer that is easily visible.
Two flat surfaces and six borders makeup the largely quadrilateral vomer. Both surfaces of the bone have a nasopalatine groove. This groove runs downward and forward in an oblique slant. The nerves and vessels of the nasal passages are contained in these areas.
A deep furrow marks the superior border, the thickest of the four. The posterior border is concave, thick above and thin below; the inferior border helps to form the crest. The longest border of the bone, the anterior border, slopes both downward and forward. Its upper part is joined with the plate of the ethmoid bone, while the lower part grooves to accommodate the nose's septal cartilage.
Mammals tend to have narrow vomers that exist as single, vertical bones that tend to bend to one side. Bony fish have flattened pairs of the bone that help to create the anterior part of fish mouths. Many species have teeth on their vomers to supplement the teeth of the jaws. Some extinct species had larger vomer teeth than jaw teeth.
Birds typically have small vomers located behind their inner nostrils. These form the upper back part of the beak. Reptiles and amphibians have narrower vomers to accommodate their larger nostrils. Their vomers also usually extend back into the jaw.
Prior to 1975, children with clef palate were sometimes treated with vomer flap surgery. This involved using vomers to reconstruct the palate and cover the cleft itself. Various other surgical methods, including the Millard procedure, have replaced this procedure.
Vomer is Latin for "ploughshare." The bone was named as such because it resembles the cutting component of the plow. Some claim that the bone can be moved by alternately hitting the roof of the mouth with the tongue while pressing the fingers between the eyebrows. No scientific data has been able to prove this theory.