Overview
The equine skull is divided into the braincase (neurocranium), which protects the brain, and the facial skeleton (viscerocranium), which forms the nose, the orbits and the mouth. It is very elongated: the face takes up most of its length, mainly to hold the long arcades of cheek teeth. On the dorsal surface of the braincase the parietal bones form an external sagittal crest that ends caudally at the nuchal crest, where the nuchal ligament attaches.
Orbit and face
- Orbit: closed by bone. The zygomatic process of the frontal bone joins the zygomatic arch to form a complete postorbital bar, unlike the dog. Dorsal to it, the supraorbital foramen transmits the nerve of the same name.
- Facial crest (crista facialis): longitudinal ridge on the lateral surface of the maxilla that continues the zygomatic arch rostrally; origin of the masseter. It is a palpable landmark for locating the maxillary sinuses.
- Infraorbital foramen (foramen infraorbitale): rostral to the facial crest; the infraorbital nerve emerges here and can be blocked at this point.
- Nasoincisive notch (incisura nasoincisiva): wide cleft between the nasal and incisive bones that gives the nostrils their mobility.
Paranasal sinuses
- Conchofrontal sinus (sinus conchofrontalis): formed by the frontal sinus and the dorsal conchal sinus, which communicate widely. It drains into the caudal maxillary sinus.
- Rostral and caudal maxillary sinuses: separated by a bony septum. The roots of the last upper cheek teeth project into them.
Teeth
- Adult dental formula: 2 × (I 3/3, C 1/1, P 3–4/3, M 3/3) = 36–44. Canines are usually absent in mares, and the first premolar (wolf tooth) is small and inconstant.
- Hypsodont cheek teeth: very long crowns that keep erupting throughout life and wear at the occlusal surface.
- Anisognathism: the upper arcade is wider than the lower, so enamel points form on the buccal edge of the upper teeth and the lingual edge of the lower teeth.
- Age: eruption and wear of the incisors are used, with a wide margin of error, to estimate age.
Clinical relevance
- Sinusitis: primary or secondary to apical infection of the upper cheek teeth whose roots lie in the maxillary sinuses; it causes unilateral, foul-smelling nasal discharge.
- Dental points: enamel points injure the mucosa of the cheeks and tongue; they are rasped down periodically.
- Skull fractures: a horse that rears and falls over backwards can fracture the base of the skull (basisphenoid bone), with neurological signs and bleeding from the nose or ears.
- Nerve blocks: the infraorbital and supraorbital nerves are anaesthetised where they leave their foramina.