# Anatomy of the Mouth: Comparative Guide for Vet Students

The anatomy of the mouth is the study of the oral cavity and its boundaries, including the lips, cheeks, vestibule, teeth, tongue, palate, tonsils, and salivary duct openings. Species differences in these structures reflect diet, prehension, and digestion, and they change how you examine, intubate, and treat each patient.

## The Basic Plan of the Oral Cavity

The oral cavity is divided into two compartments. The vestibule is the space between the lips and cheeks externally and the teeth and gums internally. The oral cavity proper lies inside the dental arches. The vestibule connects to the oral cavity proper at the commissures and behind the last molars. Vestibule depth varies widely across species and is one of the first things to assess on oral examination.

The roof of the mouth is the hard palate rostrally and the soft palate caudally. The floor is formed by the tongue and the sublingual tissues. The lateral walls are the cheeks, and the rostral boundary is the lips. The caudal boundary is the oropharyngeal isthmus, which opens into the pharynx.

Blood supply comes mainly from the maxillary artery and its branches, including the major palatine and infraorbital arteries. Venous drainage runs through the maxillary and linguofacial veins. Sensory innervation of the oral cavity is primarily from the trigeminal nerve (cranial nerve V) for the teeth, gums, palate, and rostral tongue, with the glossopharyngeal nerve (CN IX) supplying the caudal tongue and pharynx.

The oral mucosa is stratified squamous epithelium. It is keratinized in areas subject to friction, such as the hard palate and the dorsal tongue, and non-keratinized in more flexible areas. Aquaporins, membrane proteins that move water and small solutes, are expressed in oral tissues. In dogs and cats, aquaporin 3 (AQP3) localizes to the plasma membrane in squamous cell carcinoma of the skin and oral cavity, and its expression is reduced in more malignant regions of these tumors [1].

## Comparative Dental Formulas

Dental formula notation uses I (incisors), C (canines), P (premolars), and M (molars) for upper and lower quadrants. The full formula is written as upper over lower, with each number representing one side of the mouth.

**Dog (deciduous):** I 3/3, C 1/1, P 3/3 = 28 teeth.

**Dog (permanent):** I 3/3, C 1/1, P 4/4, M 2/3 = 42 teeth.

**Cat (deciduous):** I 3/3, C 1/1, P 3/2 = 26 teeth.

**Cat (permanent):** I 3/3, C 1/1, P 3/2, M 1/1 = 30 teeth.

**Horse (permanent):** I 3/3, C 1/1 (often absent in mares), P 3/3 or 4/4, M 3/3 = 36 to 44 teeth. Horses have hypsodont teeth that erupt continuously and wear at the occlusal surface.

**Ruminant (permanent):** I 0/3, C 0/1, P 3/3, M 3/3 = 32 teeth. Ruminants lack upper incisors and upper canines. They have a dental pad instead.

Deciduous teeth in dogs and cats are smaller and have sharper crowns. Retained deciduous tooth root remnants can persist and cause problems. A ten-year retrospective study of 5,432 canine medical records found 237 retained root remnants in 143 dogs, most commonly associated with the deciduous maxillary canine teeth. Periapical radiolucency occurred in 63 dogs (44.1%), and root resorption or ankylosis occurred in 54 dogs (37.8%). Yorkshire Terriers were overrepresented at 41.2% of affected patients [2]. This supports routine full-mouth radiography in dogs.

## Tongue Papillae and Tongue Types

The tongue is a muscular organ covered by mucosa. Its surface features papillae, which are projections of the epithelium and lamina propria. Papilla types include filiform, fungiform, vallate, and foliate. Filiform papillae are mechanical and give the tongue its rough texture. Fungiform, vallate, and foliate papillae contain taste buds.

**Dog:** The tongue is relatively wide and flat. Filiform papillae are prominent and give a rough dorsal surface. Fungiform papillae are scattered. Vallate papillae are present on the caudal dorsum. Dogs use the tongue for lapping water and for grooming. The tongue also plays a role in thermoregulation through panting.

**Cat:** The tongue has large, caudally directed filiform papillae that are keratinized and give a rasping texture. These papillae help with grooming and removing meat from bone. Fungiform and vallate papillae are present. Cats also have a median groove on the dorsal surface.

**Horse:** The tongue is long and mobile. It is used for prehension of food and for moving food within the mouth. The dorsal surface has filiform papillae that are less prominent than in carnivores. The tongue is important for swallowing and for manipulating the bit during riding.

**Ruminant:** The tongue is long, mobile, and covered with filiform papillae that are directed caudally. It is used to grasp grass and pull it into the mouth. The tongue is a major prehensile organ in cattle and sheep.

The tongue can be a site of disease. Canine leishmaniosis can present with an oral mass on the ventral surface of the tongue. A case report described a 12-year-old dog with a tongue mass that showed granulomatous inflammation and Leishmania amastigotes on histology [3]. This is an atypical presentation, but it shows that the tongue should be examined carefully in endemic areas.

## Hard and Soft Palate Structure

The hard palate forms the rostral roof of the mouth. It is covered by keratinized mucosa and has transverse ridges called palatine rugae. These ridges help grip food and assist in swallowing. The hard palate is supported by the palatine processes of the incisive, maxillary, and palatine bones.

The soft palate is a muscular fold that extends caudally from the hard palate. It separates the nasopharynx from the oropharynx and helps close the nasopharynx during swallowing. The soft palate contains the palatine muscles and is covered by non-keratinized mucosa.

**Dog and cat:** The soft palate is relatively short and thin. It does not extend far caudally. The hard palate has prominent rugae.

**Horse:** The soft palate is long and extends caudally to overlap the epiglottis. This arrangement means horses are obligate nasal breathers. The soft palate forms a tight seal with the epiglottis during breathing. This anatomy is why horses cannot breathe through their mouths and why they are prone to certain airway problems.

**Ruminant:** The hard palate has a dental pad rostrally, which replaces the upper incisors. The soft palate is well developed and helps with rumination.

Palate defects, such as cleft palate, occur in all species. They are most common in dogs and cats and can cause milk to enter the nasal cavity during nursing. Surgical correction is usually needed.

## Tonsils

Tonsils are lymphoid tissue located at the entrance to the pharynx. They are part of the mucosal immune system and help detect pathogens.

**Dog:** The palatine tonsils are located in the tonsillar fossae on the lateral walls of the oropharynx. They are compact and can be visualized during oral examination. The lingual tonsils are on the base of the tongue.

**Cat:** The palatine tonsils are small and located in the tonsillar fossae. They are less prominent than in dogs.

**Horse:** The palatine tonsils are located in the oropharynx. They are not as easily visualized as in dogs.

**Ruminant:** The palatine tonsils are present but small. The lingual tonsils are more developed.

Tonsillar disease is uncommon in animals but can occur. Tonsillitis in dogs can be associated with respiratory or gastrointestinal disease. Enlarged tonsils can be a sign of systemic illness.

## Salivary Glands and Duct Openings

Salivary glands produce saliva, which lubricates food, aids in swallowing, and contains enzymes for initial digestion. The major salivary glands are the parotid, mandibular, sublingual, and zygomatic glands. Minor salivary glands are scattered throughout the oral mucosa.

**Dog:** The parotid duct opens opposite the upper fourth premolar. The mandibular duct opens at the sublingual caruncle. The sublingual duct opens along the sublingual fold. The zygomatic gland is unique to carnivores and opens near the upper molars.

**Cat:** The parotid duct opens opposite the upper fourth premolar. The mandibular and sublingual ducts open at the sublingual caruncle. Cats have well-developed zygomatic glands.

**Horse:** The parotid duct opens opposite the upper third or fourth premolar. The mandibular duct opens at the sublingual caruncle. The sublingual duct opens along the sublingual fold. Horses have large parotid glands.

**Ruminant:** The parotid duct opens opposite the upper fourth premolar. The mandibular duct opens at the sublingual caruncle. The sublingual duct opens along the sublingual fold. Ruminants have large parotid glands that produce copious saliva for rumination.

Salivary duct openings are important landmarks for oral examination. They can be catheterized for diagnostic or therapeutic purposes. Sialoceles, which are accumulations of saliva in soft tissues, can occur if ducts are damaged.

## Vestibule Depth and Oral Examination Landmarks

Vestibule depth varies by species and by location. In dogs and cats, the vestibule is relatively shallow, especially around the incisors. It is deeper around the canines and molars. In horses, the vestibule is deep, especially around the cheek teeth. In ruminants, the vestibule is shallow rostrally and deeper caudally.

The depth of the vestibule affects how you examine the mouth. In dogs and cats, you can retract the lips to see the vestibule and the teeth. In horses, you need a full mouth speculum to examine the cheek teeth. In ruminants, you can examine the incisors and the dental pad easily, but the cheek teeth require a speculum.

Key landmarks for oral examination include:
1. The commissures of the lips.
2. The buccal mucosa and the parotid duct opening.
3. The gingiva and the mucogingival junction.
4. The teeth and the dental arcades.
5. The hard palate and the palatine rugae.
6. The soft palate and the oropharyngeal isthmus.
7. The tongue and its papillae.
8. The sublingual caruncle and the sublingual fold.
9. The tonsillar fossae.

## Species Comparison Table

| Feature | Dog | Cat | Horse | Ruminant |
|-----|---|---|----|-----|
| Permanent dental formula | I 3/3, C 1/1, P 4/4, M 2/3 = 42 | I 3/3, C 1/1, P 3/2, M 1/1 = 30 | I 3/3, C 1/1 (often absent in mares), P 3/3 or 4/4, M 3/3 = 36 to 44 | I 0/3, C 0/1, P 3/3, M 3/3 = 32 |
| Tongue type | Wide, flat, rough dorsal surface | Narrow, rasping filiform papillae | Long, mobile, less prominent papillae | Long, mobile, caudally directed papillae |
| Palate | Short soft palate, prominent rugae | Short soft palate, prominent rugae | Long soft palate overlapping epiglottis, obligate nasal breather | Dental pad rostrally, well-developed soft palate |
| Salivary glands | Parotid, mandibular, sublingual, zygomatic | Parotid, mandibular, sublingual, zygomatic | Parotid, mandibular, sublingual | Parotid, mandibular, sublingual |

## Clinical Relevance, Limitations and Common Mistakes

Oral examination is a core skill in veterinary practice. The anatomy of the mouth determines what you can see and what you need to use. In dogs and cats, a good light source and a retractor are often enough for a basic examination. In horses and ruminants, a speculum is needed to examine the cheek teeth.

Endotracheal intubation requires knowledge of oral anatomy. In dogs and cats, the larynx is located ventral to the soft palate. You need to pass the tube through the oral cavity, past the soft palate, and into the larynx. In horses, the soft palate overlaps the epiglottis, so you need to pass the tube through the nasal cavity or through the mouth with care. In ruminants, the oral cavity is large, and intubation is usually done through the mouth.

Dental disease is common in all species. Periodontal disease is the most common oral disease in dogs and cats. It starts with plaque and progresses to gingivitis and periodontitis. Retained deciduous teeth can cause malocclusion and periodontal disease. The study of retained root remnants found that they do not undergo resorption and may develop clinical complications [2]. This is why full-mouth radiography is recommended.

Oral tumors are common in dogs and cats. Oral malignant melanoma is the most common canine oral neoplasm [4]. Squamous cell carcinoma is also common. Frozen section biopsy is a feasible and accurate tool for diagnosing canine and feline oral tumors. A study of 27 oral tumor samples found excellent diagnostic agreement (0.915) between frozen section and formalin-fixed, paraffin-embedded methods [5]. This can help with rapid diagnosis during surgery.

Surgical margins for oral tumors are important. A study of canine oral melanomas found that surgical margins of 10 to 15 mm wide with a qualitative deep margin achieved 100% complete excision rates in the groups studied [4]. This is a useful guideline for surgical planning.

Oral microbiota is relevant for antisepsis. A study of horses found that chlorhexidine was superior to ozonized water in reducing oral cavity microbiota [6]. This is relevant for procedures that require oral antisepsis.

Common mistakes in oral examination include:
1. Not using a good light source.
2. Not examining the caudal oral cavity.
3. Not palpating the tongue and the sublingual area.
4. Not checking for retained deciduous teeth.
5. Not using radiography when indicated.
6. Not recognizing that horses are obligate nasal breathers.

Limitations of this guide: individual cases need a veterinarian. This article is educational and is not a substitute for veterinary diagnosis or treatment.

## Frequently Asked Questions

### What is the dental formula for a dog?

The permanent dental formula for a dog is I 3/3, C 1/1, P 4/4, M 2/3, for a total of 42 teeth.

### How many teeth does a cat have?

A cat has 30 permanent teeth. The formula is I 3/3, C 1/1, P 3/2, M 1/1.

### Why do horses breathe only through their noses?

Horses have a long soft palate that overlaps the epiglottis, which creates a seal that prevents mouth breathing.

### What are filiform papillae?

Filiform papillae are keratinized projections on the tongue that give it a rough texture. They are prominent in cats and dogs.

### Where do salivary ducts open in the dog?

The parotid duct opens opposite the upper fourth premolar. The mandibular and sublingual ducts open at the sublingual caruncle.

### What is the vestibule of the mouth?

The vestibule is the space between the lips and cheeks and the teeth and gums.

### Why is full-mouth radiography important in dogs?

Full-mouth radiography can detect retained deciduous tooth root remnants, which can cause periapical radiolucency and root resorption.

### What is the most common oral tumor in dogs?

Oral malignant melanoma is the most common canine oral neoplasm.

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## Sources

1. [Expression of aquaporin 3 in squamous cell carcinoma in dogs and cats.](https://pubmed.ncbi.nlm.nih.gov/42236212/)
2. [Retained Deciduous Tooth Root Remnants in Dogs: A Ten-Year Retrospective Study.](https://pubmed.ncbi.nlm.nih.gov/41762173/)
3. [Canine leishmaniosis: An atypical presentation on the tongue.](https://pubmed.ncbi.nlm.nih.gov/42736004/)
4. [Surgical Margins Required for the Complete Excision of Canine Oral Melanomas.](https://pubmed.ncbi.nlm.nih.gov/41991178/)
5. [Frozen section biopsy is a feasible and accurate tool for diagnosing canine and feline oral tumors in a private veterinary oral surgery practice.](https://pubmed.ncbi.nlm.nih.gov/42161311/)
6. [Chlorhexidine is Superior to Ozonized Water in the Reduction of the Oral Cavity Microbiota of Horses.](https://pubmed.ncbi.nlm.nih.gov/41637277/)