Horse vertebral column is the fundamental part of its skeleton. Here, I will discuss the osteological features of the horse’s vertebral column with the diagrams.
You will get the overview of the typical vertebra of a horse, the types of vertebrae, and the five classifications of the vertebrae.
What is the vertebral column in a horse?
Vertebral column: The vertebral column or columna vertebralis is a chain of median, unpaired, irregular bones that extends from the skull to the end of the tail. These bones articulate with one another to form a long column along the axial skeleton, known as the vertebral column.
However, the equine’s vertebral column is also called the spine. Here, the figure shows the horse’s vertebral column, which consists of various types of vertebral bones.
Types of vertebrae in the horse’s vertebral column
There are two types of vertebrae in the horse’s vertebral column –
- Fixed or false vertebrae, and
- Movable or true vertebrae,
Fixed vertebrae: In the horse, certain vertebrae have become fused to form a single bony mass with which the pelvic girdle articulates. Vertebrae so fused are termed fixed or false vertebrae.
However, they are distinguished from the movable and are also termed the vertebrae immobiles. Example of the fixed vertebrae: sacrum bone (formed by 5 sacral vertebrae) and articulates with the hip bone of the horse’s hind limb.
Movable vertebrae: The single or individual bones of the vertebral column are known as the movable or true vertebrae (vertebrae mobiles). Examples of the movable vertebrae: all the vertebrae except for the horse’s sacrum bone.
Classification of vertebrae in the equine/horse
The horse vertebral column is subdivided for description into five regions. They are named according to the part of the body in which the vertebrae are situated.
Thus, the vertebrae are designated as follows in the horses –
- Cervical vertebrae (vertebrae cervicales),
- Thoracic vertebrae (vertebrae thoracales),
- Lumbar vertebrae (vertebrae lumbales),
- Sacral vertebrae (vertebrae sacrales), and
- Coccygeal or caudal vertebrae (vertebrae coccygeae).
I will describe all the above-mentioned types of vertebrae from the horse’s axial skeleton. However, you will find a detailed guide to the individual types of vertebrae in horses.
Equine vertebrae number
The number of vertebrae in the horse is fairly constant in each region except the last. The table shows the number of vertebrae in the horse’s vertebral column –
| Name of the vertebrae | Number of the vertebrae |
| Cervical vertebrae | 7 |
| Thoracic vertebrae | 18 |
| Lumbar vertebrae | 6 |
| Sacral vertebrae | 5 |
| Coccygeal vertebrae | 15 – 21 |
| Total number of the vertebrae | 51 – 57 |
Vertebral formula of the horse
Thus, the horse’s vertebral formula may be expressed as follows: C7T18L6S5Cy15-21.
The vertebrae in a given region have characters by which they may be distinguished from those of other regions. However, the individual vertebrae have special characters that are more or less clearly recognizable.
Typical vertebra structure in a horse/equine
All typical vertebrae share a common structural plan, which must first be understood. The parts of a vertebra are the body, the arch, and the processes.
Body of the horse’s typical vertebra
The body or corpus vertebrae is the more or less cylindrical mass on which the other parts are constructed.
Extremities: The anterior and posterior extremities of the body are attached to the adjacent vertebrae. They are attached by intervertebral fibrocartilages and are usually convex and concave, respectively.
Surfaces: The dorsal surface is flattened and enters into the formation of the vertebral canal. However, the ventral surface of the body is laterally rounded and is related to various muscles and viscera.
Exceptions: In the thoracic region, the body of the horse’s thoracic vertebrae presents two pairs of facets (foveae costales) at the extremities. They are designed for articulation with part of the heads of two pairs of the horse’s ribs.
However, the bodies of the lumbar vertebrae of the horse are compressed dorsoventrally. Again, the bodies of the coccygeal vertebrae are longer in the horse.
The arch of the horse’s typical vertebra
The arch or arcus vertebrae is constructed on the dorsal aspect of the body. It consists originally of two lateral halves, each of which is considered to consist of a pedicle and a lamina.
The figure shows the ventral pedicle and dorsal lamina from a typical vertebra.
Pedicle: The pedicle or radix arcus vertebrae forms the lateral part of the arch. However, it is cut into in front and behind by the vertebral notches.
These notches are also known as the incisura vertebralis cranialis and caudalis. Here, the notches of two adjacent vertebrae form intervertebral foramina (foramina intervertebralia). They are designed for the passage of the horse’s spinal nerves and vessels.
However, in some vertebrae of the horses, there are complete foramina instead of notches.
Laminae: The laminae are plates that complete the arch dorsally. They unite with each other medially at the root of the spinous process.
Vertebral ring, foramen, and canal: The body and the arch of the horse’s vertebra form a bony ring that encloses the vertebral foramen (foramen vertebrale). The series of vertebral rings, together with the ligaments which unite them, enclose the vertebral canal (canalis vertebralis). However, the vertebral canal contains the spinal cord, its coverings, and its vessels.
Processes of the equine’s typical vertebra
The figure shows there are three main processes in the equine’s typical vertebra: articular, spinous, and transverse.
Articular processes in equine vertebra
The articular processes, two anterior and two posterior (processus articulares craniales, caudales). They are projected from the borders of the arch of each vertebra.
However, they present articular surfaces adapted to those of adjacent vertebrae. Again, the remaining surface is roughened for muscular and ligamentous attachment.
Spinous process of the equine vertebra
The spinous process or spine (processus spinosus) is single. It projects dorsally from the middle of the arch (where the laminae and pedicle meet).
Here, the spinous process varies greatly in form, size, and direction in different vertebrae. It furnishes attachment to muscles and ligaments.
Exceptions: The thoracic vertebrae of the horse present the longest spinous process in the series of the vertebral column. However, the horse’s lumbar vertebrae possess the quadrilateral plate type of spinous process.
Transverse processes of the equine’s typical vertebra
The transverse processes/processus transversi in the equine vertebra are two in number. They project laterally from the sides of the arch or from the junction of the arch and body.
Exceptions: In the thoracic region/horse’s thoracic vertebrae have a facet (a small articular surface) for articulation with the tubercle of a rib. They are known as the fovea costalis transversalis.
They also give attachment to muscles and ligaments. However, some vertebrae of the horses also have a ventral spine or a haemal arch.
Mammillary and accessory processes in the horse’s vertebra
The horse’s vertebrae sometimes present mammillary and accessory processes.
Mammillary processes: Mammillary processes (processus mamillares) are found in most horses on the last thoracic and anterior lumbar vertebrae. However, they are located between the transverse and anterior articular processes or on the latter.
Accessory processes: Accessory processes, or processus accessorii, may also be present in the horse’s vertebra. However, they are situated between the transverse and posterior articular processes.
FAQ’s on the horse’s vertebral column
The horse’s vertebrae are developed by ossification in the cartilage. However, they surround the notochord and form the sides of the neural canal. There are three primary centers of ossification, one for the body and one for each side of the arch. Secondary centers appear later for the summit of the spinous process (except in the cervical region). However, it also appears in the extremities of the transverse processes and the thin epiphyseal plates at the extremities of the body.
There are at first two centers for the body of the horse’s vertebrae, which soon fuse. The process of ossification extends from the lateral centers to form not only the corresponding part of the arch.
In the horse, the body and arch are fused at birth or unite very soon after, but the epiphyses do not fuse till growth is complete. In the pig, sheep, and dog, the body and arch are united at birth by cartilage, but fuse in the first few months.
There are seven (C1-C7) cervical vertebrae in the horse’s vertebral column. They are cervical I to cervical VII and are also designated C1, C2, C3, C4, C5, C6, and C7. However, the C1 is termed the atlas, whereas C2 is termed the axis vertebra.
Yes, the horses have 18 thoracic vertebrae in their axial skeleton. Here, the number of the horse’s thoracic vertebrae corresponds to the number of the horse’s ribs. However, they are designated by T1 – T18 vertebrae.
Conclusion
The horse vertebral column is an important part of the skeleton and is formed by the cervical, thoracic, lumbar, sacral, and coccygeal vertebrae. Here, the typical vertebra of a horse presents a body, arches, and three types of processes.
References
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