Cheek pouches are pockets on both sides of the head of some mammals between the jaw and the cheek. They can be found on mammals including the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

, some

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s, and most

monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, co ...

s, as well as the

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

koala The koala (''Phascolarctos cinereus''), sometimes inaccurately called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the Family (biology), family ''Phascolar ...

. The cheek pouches of

chipmunk Chipmunks are small, striped rodents of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks are classified as four genera: '' ...

s can reach the size of their body when full.

Description and function

Cheek pouches are located in the thickness of the

flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of a steel beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer o ...

on both sides of the head of some mammals. Monkeys have open cheek pouches within the oral cavity, but they open out in some rodents of America. Hence the name "diplostomes" is associated with them, which means "two mouths." In some rodents, such as

hamster Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera. They have become established as popular small pets. The best-known species of hamster is the golden or Syrian ...

s, the cheek pouches are remarkably developed; they form two bags ranging from the mouth to the front of the shoulders.

Étienne Geoffroy Saint-Hilaire Étienne Geoffroy Saint-Hilaire (; 15 April 177219 June 1844) was a French naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theorie ...

described that some bats of the genus '' Nycteris'' have an amazing form of cheek pouches, as they have a narrow opening, through which the bat can introduce air, closing the nasal canal through a special mechanism and pushing air under the skin, so they expire in the tissue, which unites the very loose skin to the underlying muscles. Cheek pouches have several roles; they allow the rapid collection of food, but also serve as temporary storage and transport. In monkeys of the subfamily of

Cercopithecinae The Cercopithecinae are a subfamily of the Old World monkeys, which comprises roughly 71 species, including the baboons, the macaques, and the vervet monkeys. Most cercopithecine monkeys are limited to sub-Saharan Africa, although the macaques ra ...

, they allow for more predigested food. Cheek pouches contribute to the protection of animals by allowing them to carry their food in the pouches to shelter, allowing them to transport their food to safer locations, as they are pressing these pouches to the back of the mouth with the back of the leg, or moving the jaw. The females of some species of hamster are known to hide their young in their cheek pouches to carry them away when they fear danger. Other species of hamsters are known to fill their pouches with air, allowing them to float better while they swim. The cheek pouches can become infected as a result of an injury caused by a sharp object inserted into them or a fight. An

abscess An abscess is a collection of pus that has built up within the tissue of the body, usually caused by bacterial infection. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pre ...

can form, which can be confused with protuberance with stored food. If the abscess bursts and the

pus Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during infections, regardless of cause. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collect ...

contained therein is absorbed by the animal, it can develop

sepsis Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...

and die of the poisonous toxins. The cheek pouches can also turn outwards. The cheek pouches of hamsters have been studied in laboratories to understand vascular membranes and healing better. They are also useful for the study of the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

, notably in the development of abscesses or

tumour A neoplasm () is a type of abnormal and excessive growth of tissue (biology), tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tiss ...

Examples

Chipmunks

Chipmunk Chipmunks are small, striped rodents of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks are classified as four genera: '' ...

s (''Tamias'') have large cheek pouches that allow them to transport food. These pouches can reach the size of their body when they are full. Below is the introduction of the

legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

(pod) of

peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), goober pea, pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics by small and large ...

in the cheek pouch of a chipmunk:

File:Chipetting6.jpg, Peanut half entered the cheek pouch File:Chipetting (say aah).jpg, Peanut during storage File:Chipmunk with peanut hidden in cheek pouch.jpg, Peanut entirely in the cheek pouch File:Peanut stash.jpg, Chipmunk in profile with cheek pouch swollen by a peanut pod

Hamsters

Backentaschen Feldhamster Cricetus cricetus cheek pouches

One of the classic behavioral characteristics of

s (subfamily Cricetinae) is food hoarding. Hamsters carry food to their underground storage chambers using their spacious cheek pouches.Fox, Sue. 2006. Hamsters. T.F.H. Publications Inc. A hamster "can literally fill its face with food." When full, the pouches can make the hamsters' heads double, or even triple in size.

Platypus

The

feeds on

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

worms, insect larvae, freshwater

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

s, and yabbies (freshwater crayfish) that it digs out of the riverbed with its snout or catches while swimming. It uses its cheek pouches to carry prey to the surface for eating.

Misconception with ''Rattus rattus''

The cheek pouch is a specific morphological feature that is evident in particular subgroups of rodents (e.g.

Heteromyidae Heteromyidae is a family of rodents consisting of kangaroo rats, kangaroo mice, pocket mice and spiny pocket mice. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the ...

and Geomyidae, or gopher), yet a common misconception is that certain families, such as

Muridae The Muridae, or murids, are either the largest or second-largest family of rodents and of mammals, containing approximately 870 species, including many species of mice, rats, and gerbils found naturally throughout Eurasia, Africa, and Australia. ...

(including the common black and brown rats), contain this structure when in fact their cheeks are merely elastic due to a high degree of musculature and

innervation A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...

in the region. The true cheek pouch, however, is evident in the former Heteromyidae and Geomyidae groups. Cheek pouches are more pronounced in certain rodents, such as hamsters, yet this structure is also distinguishable on certain species of rat, like the

Gambian pouched rat The Gambian pouched rat (''Cricetomys gambianus''), also Common name, commonly known as the African giant pouched rat, is a species of nocturnal pouched rat of the giant pouched rat genus ''Cricetomys'', in the Family (biology), family Nesomyidae ...

, of which extensive morphological investigations have been conducted. Aspects including rat pouch musculature, vascularization, and innervation were all explored and compiled through this and other studies. The widely distributed ''

Rattus rattus The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is ...

'' is an example of the rodent family Muridae that lacks a true cheek pouch; rather, they exhibit more elastic cheeks (not true pouches) due to the organization of their cheek musculature. Concerning the musculature, the cheek pouch is composed primarily of a developed

masseter In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the ...

(cheek) muscle that exhibits a high

tensile Tension is the pulling or stretching force transmitted axially along an object such as a string, rope, chain, rod, truss member, or other object, so as to stretch or pull apart the object. In terms of force, it is the opposite of ''compression ...

ability. The masseter muscle has been shown to insert into the pectoralis muscles, allowing for a higher degree of food retention. The pouch is clearly divided between a buccal (cheek) and sublingual (below the tongue) portion. Volumetric analyses within this study attributed the differences in net cheek volume between male and female rats to the average size of the respective sexes. Due to muscle's high nutritional demand, this muscle exhibits vascularization that has been highly studied. Dissections at

Boston University Boston University (BU) is a Private university, private research university in Boston, Massachusetts, United States. BU was founded in 1839 by a group of Boston Methodism, Methodists with its original campus in Newbury (town), Vermont, Newbur ...

by Frank Brodie describe the various bifurcations (or splittings) of the

common carotid In anatomy, the left and right common carotid arteries (carotids) () are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries. Structure The common carotid a ...

. This artery splits into an internal and external branch, of which the latter extends

dorsally Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

and divides into five branches that supply the general cheek region. The branch that extends dorsally to the ear is known as the auricular branch. As for innervation of this structure, the associated nerve branches were all found to originate from the facial (CN VII of XII) nerve that initiates at the medulla and passes into the

facial canal The facial canal (also known as the Fallopian canal) is a Z-shaped canal in the temporal bone of the skull. It extends between the internal acoustic meatus and stylomastoid foramen. It transmits the facial nerve (CN VII) (after which it is nam ...

via the

stylomastoid foramen The stylomastoid foramen is a foramen between the styloid and mastoid processes of the temporal bone of the skull. It is the termination of the facial canal, and transmits the facial nerve, and stylomastoid artery. Facial nerve inflammation in th ...

. The primary aforementioned muscle, the masseter, is supplied by two large neural branches known as the temporalis and

zygomatic nerve The zygomatic nerve is a branch of the maxillary nerve (itself a branch of the trigeminal nerve (CN V)). It arises in the pterygopalatine fossa and enters the orbit through the inferior orbital fissure before dividing into its two terminal branc ...

s. The buccal divisions of this nerve supply much of the masseter muscle, which ultimately facilitates the voluntary retention of food within the cheek pouch.

References

{{Commons category, Cheek pouches Rodent anatomy