Editing Perissodactyla (section)

===Skull and teeth===
[[File:Hamburg zoo tapir.JPG|thumb|Tapirs are the only extant group of perissodactyls with a trunk.]]

Odd-toed ungulates have a long [[maxilla|upper jaw]] with an extended [[diastema]] between the front and cheek [[Tooth|teeth]], giving them an elongated head. The various forms of snout between families are due to differences in the form of the [[premaxilla]]. The [[lacrimal bone]] has projecting cusps in the eye sockets and a wide contact with the nasal bone. The [[temporomandibular joint]] is high and the [[mandible]] is enlarged.

Rhinos have one or two horns made of [[wiktionary:agglutinate|agglutinated]] [[keratin]], unlike the horns of [[even-toed ungulate]]s ([[Bovidae]] and [[pronghorn]]), which have a bony core.

The number and form of the teeth vary according to diet. The [[incisor]]s and [[canine tooth|canine]]s can be very small or completely absent, as in the two African species of rhinoceros. In horses, usually only the males possess canines. The surface shape and height of the [[Molar (tooth)|molars]] is heavily dependent on whether soft leaves or hard grass make up the main component of their diets. Three or four cheek teeth are present on each jaw half, so the [[Dentition|dental formula]] of odd-toed ungulates is: 
{{DentalFormula |upper= 0-3 . 0-1 . 2-4 . 3|lower= 1-3 . 1 . 2-4 . 3|total= 30-44}}

The [[guttural pouch]], a small outpocketing of the [[Eustachian tube|auditory tube]] that drains the [[middle ear]], is a characteristic feature of Perissodactyla.<ref name="Singh-2018">{{cite book |last1=Singh |first1=Baljit |title=Dyce, Sack and Wensing's Textbook of Veterinary Anatomy |date=2018 |publisher=Elsevier |location=Missouri |isbn=978-0-323442640 |page=511 |edition=5th}}</ref> The guttural pouch is of particular concern in [[Equinae|equine]] [[Veterinarian|veterinary practice]], due to its frequent involvement in some serious infections. [[Aspergillosis]] (infection with ''Aspergillus'' mould) of the guttural pouch (also called [[Guttural pouch#Guttural Pouch Mycosis|guttural pouch mycosis]]) can cause serious damage to the tissues of the pouch, as well as surrounding structures including important [[cranial nerves]] (nerves IX-XII: [[Glossopharyngeal nerve|glossopharyngeal]], [[Vagus nerve|vagus]], [[Accessory nerve|accessory]] and [[Hypoglossal nerve|hypoglossal nerves]]<ref name="Singh-2018" />) and the [[internal carotid artery]].<ref name="Singh-2018" /> [[Strangles]] (''Streptococcus equi equi'' infection) is a highly transmissible respiratory infection of horses<ref>{{cite web |last1=Rush |first1=Bonnie |title=Strangles (Distemper) in Horses - MSD Veterinary Manual |url=https://www.msdvetmanual.com/horse-owners/lung-and-airway-disorders-of-horses/strangles-distemper-in-horses |website=MSD Veterinary Manual |publisher=MSD |access-date=25 September 2023}}</ref><ref>{{cite web |last1=Lascola |first1=Kara |title=Strangles in Horses - Respiratory Diseases of Horses - MSD Veterinary Manual |url=https://www.msdvetmanual.com/respiratory-system/respiratory-diseases-of-horses/strangles-in-horses |website=MSD Veterinary Manual |publisher=MSD |access-date=25 September 2023}}</ref> that can cause pus to accumulate in the guttural pouch;<ref>{{cite book |last1=Singh |first1=Baljit |title=Dyce, Sack and Wensing's Textbook of Veterinary Anatomy |date=2018 |publisher=Elsevier |location=Missouri |isbn=978-0-323442640 |page=512 |edition=5th}}</ref> horses with ''S. equi equi'' colonising their guttural pouch can continue to intermittently shed the bacteria for several months,<ref>{{cite web |last1=Freeman |first1=Paul |title=Strangles |url=https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0011/158456/Strangles.pdf |website=Strangles |publisher=NSW Government - Department of Primary Industries |access-date=25 September 2023}}</ref> and should be isolated from other horses during this time to prevent transmission. Due to the intermittent nature of ''S. equi equi'' shedding, prematurely reintroducing an infected horse may risk exposing other horses to the infection, even though the shedding horse appears well and may have previously returned negative samples. The function of the guttural pouch has been difficult to determine, but it is now believed to play a role in cooling blood in the internal carotid artery before it enters the brain.<ref name="Singh-2018" />