The isthmus of the fauces or the oropharyngeal isthmus is a part of the oropharynx

Oropharynx

The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....

 directly behind the mouth cavity, bounded superiorly by the soft palate

Soft palate

The soft palate is the soft tissue constituting the back of the roof of the mouth. The soft palate is distinguished from the hard palate at the front of the mouth in that it does not contain bone....

, laterally by the palatoglossal arch

Palatoglossal arch

The palatoglossal arch on either side runs downward, lateralward, and forward to the side of the base of the tongue, and is formed by the projection of the glossopalatine muscle with its covering mucous membrane. It is the anterior border of isthmus faucium and marks the border between the mouth...

es, and inferiorly by the tongue

Tongue

The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...

.

The fauces are regarded as the two pillars, formed by the palatoglossus

Palatoglossus muscle

The palatoglossus, glossopalatinus, or palatoglossal muscle is a small fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the glossopalatine arch....

 and the palatopharyngeus muscle

Palatopharyngeus muscle

The palatopharyngeus or palatopharyngeal or pharyngopalatinus muscle is a long, fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the palatopharyngeal arch.-Origin and insertion:...

, respectively, and covered with mucous membrane

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

. The anterior one is known as the palatoglossal arch

Palatoglossal arch

The palatoglossal arch on either side runs downward, lateralward, and forward to the side of the base of the tongue, and is formed by the projection of the glossopalatine muscle with its covering mucous membrane. It is the anterior border of isthmus faucium and marks the border between the mouth...

, and the posterior one is known as the palatopharyngeal arch

Palatopharyngeal arch

The palatopharyngeal arch is larger and projects farther toward the middle line than the anterior; it runs downward, lateralward, and backward to the side of the pharynx, and is formed by the projection of the Pharyngopalatinus, covered by mucous membrane....

. Between these two arches is the palatine tonsil.

Each palatoglossal arch runs downwards, laterally and forwards, from the soft palate to the side of the tongue. The approximation of the arches due to the contraction of the palatoglossal muscles constricts the isthmus, and is essential to swallowing

Swallowing

Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration...

 (deglutition).

Faucitis

Inflammation of the fauces is known as faucitis and is seen in animals. In cats, faucitis is usually a secondary disease to gingivitis

Gingivitis

Gingivitis is a term used to describe non-destructive periodontal disease. The most common form of gingivitis is in response to bacterial biofilms adherent to tooth surfaces, termed plaque-induced gingivitis, and is the most common form of periodontal disease...

), but can be a primary disease. In this species, faucitis is usually caused by bacterial and viral infections although food allergies

Food allergy

A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions....

 need to be excluded in any diagnosis. Treatment is symptomatic

Symptomatic treatment

Symptomatic treatment is any medical therapy of a disease that only affects its symptoms, not its cause, i.e., its etiology. It is usually aimed at reducing the signs and symptoms for the comfort and well-being of the patient, but it also may be useful in reducing organic consequences and sequelae...

 and includes broad-spectrum antibiotic

Broad-spectrum antibiotic

The term broad-spectrum antibiotic refers to an antibiotic that acts against a wide range of disease-causing bacteria. A broad-spectrum antibiotic acts against both Gram-positive and Gram-negative bacteria, in contrast to a narrow-spectrum antibiotic, which is effective against specific families of...

s and in severe cases where cats are inappetant, corticosteroid

Corticosteroid

Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...

s (often given as depot forms, e.g. depomedrol 20mg SQ stat) or chemotherapy

Chemotherapy

Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....

 (e.g. chlorambucil

Chlorambucil

Chlorambucil is a chemotherapy drug that has been mainly used in the treatment of chronic lymphocytic leukemia...

2mg every 3 days).