Equine Spine and Head Anatomy

Original Editor - Chelsea McLene

Top Contributors - Chelsea Mclene, Tarina van der Stockt, Jess Bell and Kim Jackson  

Introduction

Equine anatomy refers to the gross and microscopic anatomy of horses and other equids, including donkeys, and zebras.

Axial skeleton

The axial skeleton consist of skull, vertebral column, sternum, and ribs. Multiple sternebrae fuse to form one bone, attached to the 8 "true" pairs of ribs, out of a total of 18.

The vertebral column contains 54 bones:

• 7 Cervical vertebrae: includes the atlas (C1) and axis (C2)
• 18-19 Thoracic vertebrae
• 5-6 Lumbar vertebrae
• 5 Sacral vertebrae
• 15-25 Caudal vertebrae

In certain breeds, there may be difference in the number.

Skull

The skull consists of the brain and the most important organs of sense including bones and cavities.

Bones in the equine skull

There are 34 bones and most of them are flat. During the birth process, these bones overlap, and allow skull to compress as much as possible while it allows easy parturition.

14 Major bones:

• Incisive bone (premaxillary): part of the upper jaw; where the incisors attach
• Nasal bone: covers the nasal cavity
• Maxillary bone: a large bone that contains the roots of the molars
• Mandible: lower portion of the jaw; largest bone in the skull
• Lacrimal bone: contains the nasolacrimal duct, which carries fluid from the surface of the eye, to the nose
• Frontal bone: creates the forehead of the horse
• Parietal bone: extends from the forehead to the back of the skull
• Occipital bone: forms the joint between the skull and the first vertebrae of the neck (the atlas)
• Temporal bone: contains the eternal acoustic meatus, which transmits sound from the ear to the cochlea (eardrum)
• Zygomatic bone: attaches to the temporal bone to form the zygomatic arch (cheek bone)
• Palatine bone: forms the back of the hard palate
• Sphenoid: formed by fusion of the foetal basisphenoid and presphenoid bones, at the base of the skull. Can become fractured in horses that rear over backwards.
• Vomer: forms the top of the inside of the nasal cavity
• Pterygoid: small bone attached to the sphenoid that extends downward

Cavities

The Equine skull consists of 4 cavities:

• The cranial cavity: Protects and encloses the brain, supports sense organs.
• The orbital cavity: Protects and surround the eye. They have unique eyes :
  • Monocular vision: The horse can see objects with one eye. This means that the brain receives two images simultaneously.
  • Binocular vision: The horse can focus with both eyes just like humans and the brain is receives only one signal.
• The oral cavity: It is a passage into the respiratory and digestive system.
• The nasal cavity: contains bone that protects mucous membrane from inspired warm air.