The equine skull consists of 34 large and small bones. Occlusal crown morphology (i.e., shape and disappearance of dental stars) has been studied as an indicator of age in horses.
Muscles are organized in pairs that oppose each other, and act on the bones they’re attached to in order to bend or extend them.
The horse boasts one of the largest eyes among land mammals. Unfortunately, this makes them vulnerable to eye injuries, particularly corneal ulcers (caused by loss of top layer of cornea). Their large eyes located on either side of their heads allow them to see more than predators with eyes located directly in front of their faces; however, horses cannot see directly behind or in front of themselves.
Eye anatomy consists of several main components. On its interior lies the lens, iris and pupil (which allow light into the eye). A ciliary body surrounds the lens to control its shape and therefore how distant or near objects appear. Outside lies the retina which features reflective regions known as tapetum lucidum and sends visual information directly to your brain via optic nerves.
Horse’s upper and lower eyelids provide protection from eyeball damage, with reflexive blinks to spread tears over the lens surface to keep it moist and clear away small particles. In addition, their third eyelid – known as the Nictitating Membrane – extends over their eyeball when necessary and protects from scratching from foreign objects or debris in their environment as well as helping detect peripheral motion more quickly than with just two lids alone.
Ears contain an intricate network of muscles that enable them to move in various ways, making horses’ ears relatively straightforward to interpret as they are large and visible. Furthermore, their movements can easily be observed unlike some facial expressions where certain aspects may be obscured by head movement.
Horse ears use muscles to rotate and pull on the pinna. This causes its ears to look as though it’s being pulled forward, possibly producing sound when pulled. A horse may also use its muscles to bob its ear back and forth – often seen as head shaking but possibly also used as a signal that something has changed emotionally or environmentally.
EquiFACS records all possible facial movements in horses using an objective, anatomically-based coding method used in humans, chimpanzees (Pan troglodytes), orangutans (Pongo pygmaeus), rhesus macaques (Macaca mulatta), dogs (Canis familiaris) and cats (Felis catus). This allows direct comparisons across species with similar muscle anatomy; previous studies only investigated specific expressions like pain when looking at specific expressions; while EquiFACS presents all possibilities a horse could make in terms of all potential faces that it could make.
Equine faces feature well-developed jaw structures that enable wide facial movements. Horses possess an extensive network of robust muscles whose tendon connections converge in the lower face and lips for complex innervation; particularly thick tissues can be found around ears, lips and noses of horses.
HORSES and POLARIS differ from dogs in that their zygomatic arches are fully developed, with an abundance of facial tuberosity visible at their rostrums. Upper cheek teeth fuse to the palatine bone in order to form the bicuspid teeth; on the contrary, lower cheek teeth typically feature diastema or diastemae (i.e. bars). When young, permanent canines P3 and P4 may develop deciduous canines; these may appear as small protrusions visible near their ventral edges; known as deciduous canines on young horses’ skulls or protrusions from ventral edges of mandibles.
The basihyoid’s lingual process extends caudodorsally, where it articulates with the thyroid cartilage of the larynx, and dorsally to connect with stylohyoids that create compartments in guttural pouches of the tongue. Furthermore, some have speculated that its extension provides attachment points for tricuspid teeth, but this has yet to be proven by direct histological examination of cadaver heads.
The neck of a horse serves as an integral connector between its head and body, with its shape, movement, and position having profound implications on balance, center of gravity, and motion in general.
The bones of the neck are arranged in an S-shape, with its top curve situated just behind the head and its bottom curve connecting with one long spine vertebrae (known as thoracic vertebrae) located within each shoulder region. This gives strength and flexibility to the neck structure.
There are seven neck vertebrae, but two stand out in both form and function from the rest. The atlas connects directly to the back of the skull for up-and-down movements (some people refer to it as the yes joint). Meanwhile, another cervical vertebra is built differently and allows side to side movements for horses as they flex at their poll and bring their nose closer to their chest while moving their neck.
Other skull bones include the frontal bone, parietal bone, zygomatic arch, vomer and palatine foramen. Salivary glands with ducts leading into the oral cavity include parotid glands on each cheek lateral to Viborg’s triangle; other species do not possess this gland. Also, facial tuberosities complete each side of each zygomatic arch laterally while DOG does not possess one at all.