In the equids and some rodent-like species such as the desert hyrax

Hyrax

A hyrax is any of four species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. The rock hyrax Procavia capensis, the yellow-spotted rock hyrax Heterohyrax brucei, the western tree hyrax Dendrohyrax dorsalis, and the southern tree hyrax, Dendrohyrax arboreus live in Africa...

, the guttural pouch is a pair of air chambers in the neck just behind the skull and below the ears. These pouches are on both sides of the head and are air-filled out-pouching or evagination to the Eustachian tube, leading into the trachea

Vertebrate trachea

In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

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While the location of the pouches is generally understood, their purpose is not. Currently, researchers believe the pouches serve to cool blood flow to the brain during extended strenuous exercise.

Due to the general inaccessibility of the pouches, they can be an area of infection by molds and bacteria, and these infections can be extremely severe and hard to treat. The condition Guttural pouch tympany affects several breeds, including the Arabian horse

Arabian horse

The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses...

. The condition predisposes young horses to infection, often including severe swelling and often requires surgery to correct.