The vomer is a thin, unpaired bone that forms the lower and back portion of the nasal septum, the wall dividing the left and right sides of your nose. It is one of the smallest bones in the skull, yet it sits at the intersection of several fascinating topics: prenatal skull development, pheromone detection across the animal kingdom, the evolutionary loss of chemical sensing in humans, and modern surgical techniques for cleft palate repair. Its name comes from the Latin word for “plowshare,” a reference to its flat, blade-like shape.
Where the Vomer Sits and What It Does
The vomer occupies a central position in the skull. Its upper edge connects to the bottom of a plate of the sphenoid bone (the bone that spans the base of the skull behind your eyes), while its lower edge rests on the bony ridge formed by the maxillae and palatine bones, the bones that make up your hard palate. The front edge of the vomer meets the septal cartilage of the nose, and its back edge forms the dividing line you can see if you look straight into the back of someone’s nasal cavity. Together with the perpendicular plate of the ethmoid bone above it and the cartilaginous septum in front, the vomer helps create the rigid partition that keeps the two nasal passages separate.
Because the vomer is covered in mucosa on both sides, surgeons sometimes harvest that tissue as a flap during sinus procedures. A technique using the vascularized mucosa of the vomer’s rostrum (its beak-like front projection) and posterior septum can cover exposed bone after wide sphenoid sinus surgery, reducing healing complications.
How the Vomer Forms Before Birth
Unlike many skull bones that develop from cartilage templates, the vomer forms through a process called intramembranous ossification, meaning bone tissue develops directly within a membrane rather than replacing a cartilage model. A study mapping prenatal skull development found that the vomer’s very first sign of ossification appears as two separate centers, one on each side of the cartilaginous nasal septum, and this happens before the nasal bones even begin to harden.1PubMed. The prenatal development of the human nasal and vomeral bones Those two ossification centers gradually fuse along their bottom edges beneath the septum cartilage, forming a U-shaped trough when viewed in cross-section. As more bone is deposited along the bottom of that trough, the shape changes from a U into a Y, and eventually into the thin flat blade seen in adults.
This developmental sequence is remarkably consistent across mammals. Research on sheep fetuses documented essentially the same pattern: two bilateral ossification centers appearing early in fetal life, forming through intramembranous ossification in the membrane surrounding the cartilaginous nasal capsule.2Basrah Journal of Veterinary Research. MORPHOMETRICAL STUDY FOR DEVELOPMENT OF VOMER BONE IN INDIGENOUS SHEEP FETUSES The conservation of this developmental blueprint across species separated by tens of millions of years of evolution underscores how fundamental the nasal septum architecture is to breathing and skull structure in mammals.
The Vomer Across Vertebrate Evolution
In the broader story of vertebrate evolution, the vomer has played a much larger role than simply dividing the nasal cavity. In early land-dwelling vertebrates (tetrapods), the vomer was a substantial bone on the palate, often bearing teeth and contributing to the roof of the mouth. A study tracing changes in palate bones across the tetrapod family tree found that the vomer’s size and shape evolved in divergent directions from a moderate ancestral condition: some lineages, like the temnospondyls (large early amphibians), evolved substantially larger vomers, while the lineage leading toward reptiles and mammals evolved progressively smaller ones.3PubMed Central. Linked morphological changes during palate evolution in early tetrapods
In modern mammals, the vomer has been reduced to the thin septal blade we know today. Reptiles, amphibians, and fish, by contrast, retain vomers that are more prominent palate bones and may still carry teeth. If you have ever seen a snake’s skull, the vomers are paired bones flanking the front of the palate, positioned right above the openings that lead to the vomeronasal organs. That anatomical relationship between the vomer and the vomeronasal organ is ancient and is what gives the organ its name.
The Vomeronasal Organ and Chemical Sensing
The vomeronasal organ, also called Jacobson’s organ, is a small tubular structure located in the mucosa of the nasal septum, typically near the base of the vomer.4PubMed Central. The Human Vomeronasal (Jacobson’s) Organ: A Short Review of Current Conceptions, With an English Translation of Potiquet’s Original Text In many mammals, reptiles, and amphibians, it functions as a dedicated chemical-sensing system separate from the main olfactory system in the nose. While your regular sense of smell picks up airborne odors and helps you identify food, danger, or a familiar place, the vomeronasal organ in animals that use it is tuned more specifically to pheromones and other chemical signals from members of the same species.
These vomeronasal organs are paired structures, sitting bilaterally in the nasal septum mucosa.5PubMed. The human vomeronasal organ. V. An interpretation of its discovery by Ruysch, Jacobson, or Kölliker, with an English translation of Kölliker (1877) In a rodent like a mouse, they are lined with sensory neurons that detect specific chemical cues and relay that information to a dedicated brain region called the accessory olfactory bulb, which is distinct from the main olfactory bulb that processes ordinary smells. The sensory neurons in the vomeronasal organ project their axons to the accessory olfactory bulb, where they form connections with relay neurons called mitral cells.6PubMed Central. Activity regulates functional connectivity from the vomeronasal organ to the accessory olfactory bulb From there, signals travel deeper into the brain, influencing behaviors related to mating, aggression, and social recognition.
The vomeronasal organ does not handle all pheromone-related responses on its own. Research has shown that it mediates responses to some, but not all, pheromone-like signals, meaning the main olfactory system also plays a role in detecting certain chemical cues between animals.7PubMed. Pheromones, the vomeronasal system, and communication. From hormonal responses to individual recognition
How Snakes Use Tongue-Flicking to Smell
Snakes are among the most dramatic users of the vomeronasal system. Because snakes lack external ears and have relatively poor eyesight in many species, chemical sensing is their primary way of navigating the world. They deliver odor molecules to the vomeronasal organ by flicking their tongues.8PubMed. Neural substrates for tongue-flicking behavior in snakes Each flick picks up chemical particles from the air or ground, and when the tongue retracts, its forked tips deposit those particles into the paired openings of the vomeronasal organs on the roof of the mouth, directly above the vomer bones.
The forked shape of a snake’s tongue is not accidental. Research supports the idea that the fork allows the snake to sample two points in a chemical gradient simultaneously, functioning as a kind of stereo chemical detector. By comparing the concentration of a scent on the left tip versus the right tip, a snake can determine instantly which direction a pheromone trail or prey scent is coming from.9PubMed. Why snakes have forked tongues This gives snakes an edge in tracking prey and finding mates that would be difficult to achieve with a single-tipped tongue sampling one point at a time.
The Molecular Channel That Makes Pheromone Sensing Work
At the molecular level, pheromone detection in the vomeronasal organ depends on a specific signaling chain. Sensory neurons in the organ carry specialized receptors on their dendrites. In mice, these receptors fall into two main families, called V1Rs and V2Rs, which detect different classes of chemical signals. When a pheromone molecule binds to one of these receptors, it triggers a cascade inside the cell that ultimately opens an ion channel called TRPC2, allowing charged particles to rush in and generate an electrical signal.10PubMed. TRPC2: molecular biology and functional importance
Experiments knocking out the TRPC2 gene in mice produced striking results. Without a functional TRPC2 channel, the primary electrical response to pheromones in vomeronasal neurons was severely impaired.11PubMed. A diacylglycerol-gated cation channel in vomeronasal neuron dendrites is impaired in TRPC2 mutant mice These mice showed dramatic behavioral changes: males failed to show aggression toward rival males and attempted to mate with both males and females indiscriminately, while females showed reduced maternal aggression.12PubMed. The TRPC2 ion channel and pheromone sensing in the accessory olfactory system The mice could still smell ordinary odors perfectly well, but the specific social and sexual behaviors driven by pheromones fell apart. TRPC2 is, in effect, the gateway through which pheromone information enters the brain’s accessory olfactory circuit.
The wiring downstream from the vomeronasal organ is organized differently from the main olfactory system. Sensory neurons expressing a given receptor gene project their axons to multiple small clusters of synapses (around six to ten per receptor type) distributed across the accessory olfactory bulb, rather than converging on a single point as main olfactory neurons do.13PubMed. A divergent pattern of sensory axonal projections is rendered convergent by second-order neurons in the accessory olfactory bulb Relay neurons in the accessory olfactory bulb then integrate those scattered inputs and pass the processed signal along to deeper brain structures involved in social behavior and hormonal regulation.
Why Humans Lost Functional Pheromone Sensing
Humans still have a vomeronasal structure. Anatomical surveys consistently find a small pit or tube in the nasal septum mucosa of most adults. But the consensus among researchers is that this structure is a leftover, not a working organ. A review of the evidence concluded that although the vomeronasal organ is found in the vast majority of human adults, it probably has no function in chemoreception.14PubMed Central. The clinical significance of the human vomeronasal organ The tissue lacks the sensory neurons and neural connections seen in species with functional organs.
The genetic evidence for this loss is compelling. The TRPC2 gene, which as described above is essential for pheromone signaling in mice, is a pseudogene in humans, meaning it carries mutations that prevent it from producing a working protein. Analysis of TRPC2 sequences across 15 primate species showed that the gene was likely functional in the common ancestor of New World monkeys and Old World monkeys and apes, but then lost its function in the common ancestor of Old World monkeys and apes.15PubMed Central. Relaxed selective pressure on an essential component of pheromone transduction in primate evolution A separate study examining both TRPC2 and the V1R pheromone receptor genes confirmed that these components of the vomeronasal signaling pathway have been deteriorating since roughly 23 million years ago, around the time the lineages leading to Old World monkeys and apes diverged, and that random inactivation of pheromone receptor genes is still ongoing in modern humans.16PubMed Central. Evolutionary deterioration of the vomeronasal pheromone transduction pathway in catarrhine primates
Not all primates have lost their vomeronasal molecular toolkit. Researchers identified the first functional V2R receptor genes in a primate, the grey mouse lemur, and confirmed their expression in the animal’s vomeronasal organ.17PubMed Central. First evidence for functional vomeronasal 2 receptor genes in primates Mouse lemurs are strepsirrhine primates, the group that split from the lineage leading to monkeys and apes much earlier in primate evolution. Their retention of working vomeronasal receptor genes is consistent with the timeline established by the TRPC2 studies: the system was still working before the Old World monkey and ape lineage diverged, so earlier-branching primates may retain it.
The question people often ask is whether humans can still detect pheromones through some other route. The answer is complicated. Humans can detect body odors that influence mood and attraction, and the main olfactory system handles that. But the dedicated pheromone circuit that drives instinctive mating and aggression behaviors in rodents and reptiles appears to be genuinely gone in humans. We smell social cues, but we process them through the same system we use to smell coffee or rain, not through a specialized pheromone pathway.
The Vomer in Cleft Palate Surgery
The vomer’s clinical relevance extends well beyond its connection to sensory evolution. In children born with cleft palates, the vomer is one of the most important surgical landmarks. A cleft palate occurs when the two halves of the palate fail to fuse during fetal development, leaving a gap that connects the mouth and nasal cavity. Because the vomer sits right at the midline where the nasal septum meets the palate, and because it is covered in well-vascularized mucosa, surgeons can raise a flap of tissue from the vomer to help close the cleft.
A comprehensive review of vomer flap techniques identified three main approaches for unilateral clefts (clefts on one side): flaps based on the top of the vomer, flaps based on the bottom, and “open-book” flaps that unfold the vomer’s mucosal covering. For bilateral clefts (both sides), flaps based on the top of the vomer and the open-book configuration produced better results, with lower rates of fistula formation (a hole that reopens after surgery) compared to bottom-based flaps. The vomer flap is particularly useful in early repairs and in wide clefts where other tissue may not stretch far enough.18PubMed. The Vomer Flap in Cleft Palate Repair: A Comprehensive Review of Indications, Techniques, and Outcomes
One concern surgeons have had is whether manipulating the vomer early in life might restrict growth of the upper jaw. The available evidence suggests the effect on maxillary development is minimal, which has made early vomer flap repair an increasingly popular approach. A study evaluating the reliability of vomer flaps placed at the time of primary lip repair (one of the earliest surgical interventions for cleft patients) found that the flap remained intact in about 94% of cases when checked at later surgery. The small number of failures all occurred with a specific suturing technique that has since been abandoned in favor of a method that attaches the flap to the raw surface of the oral mucosa rather than directly to the nasal mucosa.19PubMed. How reliable is the vomer flap in early hard palate repair? The fact that vomerine tissue sits right next to the palatal defect and is easy to mobilize makes it a practical choice for augmenting cleft repairs.20PubMed. Use of vomer flap in palatoplasty: revisited
Nasal Obstruction and Vomer Bone Spurs
Outside of cleft surgery, the vomer can cause problems when it develops abnormally. A nasal septal spur is a sharp bony projection that juts out from the septum into one of the nasal passages, and it commonly arises from the vomer or the junction between the vomer and the perpendicular plate of the ethmoid. These spurs can cause chronic one-sided nasal obstruction, headaches from contact with the lateral nasal wall, and sometimes recurrent nosebleeds.
Traditional septoplasty, the standard surgery for a deviated septum, involves lifting the mucosa off the cartilage and bone, removing or reshaping the deviated sections, and laying the mucosa back down. For isolated bony spurs originating from the vomer, a less invasive option has gained ground. A study evaluating endoscopic electric drilling for nasal septal spurs of the vomer found that patients’ nasal obstruction scores dropped from roughly 70 out of 100 before surgery to about 15 after, indicating substantial relief. The technique was associated with minimal bleeding and a low complication rate.21مجلة جامعة صنعاء للطب والعلوم الصحية. Endoscopic Electric Drilling in the Correction of Nasal Septal Spur of the Vomer Because the drilling targets only the bony spur without requiring the extensive tissue elevation of a full septoplasty, recovery tends to be faster and the risk of septal perforation is lower.
Vomer Shape and Facial Structure
The vomer does not exist in isolation from the rest of the face. Because it connects the nasal septum to the palate and the skull base, its shape can reflect and potentially influence overall facial proportions. Research using three-dimensional imaging has examined how vomer bone dimensions vary among people with different types of jaw relationships. Using cone-beam CT scans, investigators built 3D reconstructive models of the vomer and measured its dimensions in patients with different skeletal patterns, finding measurable variation in the bone’s shape across groups with different jaw alignments.22Journal of Marmara University Institute of Health Sciences. The Vomer Bone Pattern Variations in Dentofacial Discrepancy using three-dimensional Analysis
This kind of research is still in early stages, but it points toward a broader understanding of how the bones of the midface are structurally linked. The vomer is sandwiched between the sphenoid above, the maxillae and palatines below, and the ethmoid behind. Changes in any of those neighboring bones during growth can alter the vomer’s shape, and vice versa. For orthodontists and craniofacial surgeons, appreciating how the vomer fits into the larger geometry of the face matters when planning interventions that affect the palate, the nasal septum, or the skull base. A bone that most people have never heard of turns out to sit at one of the most structurally interconnected crossroads in the human skull.