Skeletal System of The Horse - Axial Skeleton

Axial Skeleton

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

The vertebral column usually contains 54 bones: 7 cervical vertebrae, including the atlas (C1) and axis (C2) which support and help move the skull, 18 (or rarely, 19) thoracic, 5-6 lumbar, 5 sacral (which fuse together to form the sacrum), and 15-25 caudal vertebrae with an average of 18. Differences in number may occur, particularly in certain breeds. For example, some, though not all, Arabians, may have 5 lumbar vertebrae, opposed to the usual 6, 17 thoracic vertebrae (and ribs) instead of 18, and 16 or 17 caudal vertebrae instead of 18. The withers of the horse are made up by the dorsal spinal processes of the thoracic vertebrae numbers 5 to 9.

The skull consists of 34 bones and contains four cavities: the cranial cavity, the orbital cavity, oral, and the nasal cavity. The cranial cavity encloses and protects the brain and it supports several sense organs. The orbital cavitity surrounds and protects the eye. The oral cavity is a passage way into the respiratory and digestive systems. The nasal cavity leads into the respiratory system, and includes extensive paranasal sinuses. The nasal cavity contains turbinate bones that protect the mucous membrane that lines the cavity from warm inspired air. The skull consists of fourteen major bones

1. Incisive bone (premaxillary): part of the upper jaw; where the incisors attach
2. Nasal bone: covers the nasal cavity
3. Maxillary bone: a large bone that contains the roots of the molars
4. Mandible: lower portion of the jaw; largest bone in the skull
5. Lacrimal bone: contains the nasolacrimal duct, which carries fluid from the surface of the eye, to the nose
6. Frontal bone: creates the forehead of the horse
7. Parietal bone: extends from the forehead to the back of the skull
8. Occipital bone: forms the joint between the skull and the first vertebrae of the neck (the atlas)
9. Temporal bone: contains the eternal acoustic meatus, which transmits sound from the ear to the cochlea (eardrum)
10. Zygomatic bone: attaches to the temporal bone to form the zygomatic arch (cheek bone)
11. Palatine bone: forms the back of the hard palate
12. 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.
13. Vomer: forms the top of the inside of the nasal cavity
14. Pterygoid: small bone attached to the sphenoid that extends downward