Anatomy of Lumbar Vertebrae in Animals

The lumbar vertebrae are the bones of the lower back, situated between the thoracic and sacral regions of the vertebral column. They are typically larger and stronger than other vertebrae, as they bear more body weight and allow a certain degree of flexibility.

The number and structure of lumbar vertebrae vary among animal species, and these differences are often related to posture, movement, and function.

Lumbar Vertebrae of Ox

The lumbar vertebrae of ox are six in number and are characterized by greatly elongated transverse processes and strongly curved articular processes.

Body

The body is constricted in the middle, expanded at the extremities, and much compressed from above downwards.

The anterior extremity is less convex, and the posterior less concave. The arches of the first three are about equal in size and similar to the last dorsal, but behind, they gradually increase in breadth and height.

The posterior notches are much deeper. The intervertebral foramina are often double in the anterior and are very large further back.

Processes

The articular processes are large. They are placed a little further apart and are strongly curved.

The anterior articular processes are concave, directed medially, and show the mammillary processes on their lateral aspect.

The posterior articular processes are convex, directed outwards, and project from the arch at the base of the superior spine.

The transverse processes are elongated plates, flattened from above downwards, and project outwards at right angles to the body.

The processes are all directed forwards. They are shortest in the first, and the length gradually increases to the fifth; in the sixth, they are shorter than those of the fifth. The inter-transverse spaces on either side are filled up by the intertransversales lumborum muscles in life.

The spines are broad, flattened plates, resemble the last thoracic, and are of the same height as the last dorsal. That of the last is the narrowest of all. The ventral spines are rudimentary and afford attachment to the ventral longitudinal ligament.

Comparative Anatomy of Lumbar Vertebrae

While the basic structure of lumbar vertebrae is similar across mammals, there are distinct variations in their number, shape, and orientation depending on the species.

Sheep and Goat

• Lumbar vertebrae are six or seven in number in sheep and goats. In some cases, there is an ambiguous vertebra at the junction of the thoracic and lumbar regions.
• The anterior articular processes are strongly curved and overlap the posterior ones.
• The transverse processes curve forward and have expanded ends.

Horse

• Lumbar vertebrae are six in number in horses.
• The bodies are shorter.
• The first three have a distinct ventral spine, which subsides thereafter.
• The transverse process increases in length from the first to the third or fourth and then diminishes. The first one or two slightly curve backwards, and the last two or three curve forwards; the third is at right angles.
• The posterior border of the transverse process of the fifth, at its medial part, has an oval concave facet which articulates with a convex facet on the anterior border of the sixth transverse process. Sometimes the fifth has a small facet for the fourth also.
• The sixth transverse processes are thick at the base, thin and narrow elsewhere, and curve forwards. It articulates by a large concave facet on its posterior border with the corresponding facet of the sacrum.

Pig

• Lumbar vertebrae are six or seven in number in pigs.
• The bodies are longer and bear a ventral crest.
• The arches are deeply notched and are separated by an increasing space dorsally.
• The mammillary processes project outward and backward.
• The transverse processes do not articulate with each other or with the sacrum.
• The posterior edge of the root of the transverse process is marked by a notch in the anterior series and a foramen in the posterior part.
• The dorsal spines are broad and incline forward, except the last, which is narrow and vertical.

Dog

• Lumbar vertebrae are seven in number in dogs.
• Their bodies increase in width from the first to the last.
• The transverse processes are plate-like and are directed forward and downward. They do not form any joints with each other or with the sacrum as in the horse.
• Accessory and mammillary processes are present.
• The spinous processes incline a little forward.

Rabbit

• Lumbar vertebrae are seven in number in rabbits.
• The transverse processes are long and project anteriorly.

Fowl

• The lumbar and sacrum are fused and called lumbosacrals in fowl.
• They are fourteen in number, and these, with the seventh dorsal and the first coccygeal—altogether 16—are fused into one mass called the synsacrum. This forms a rhomboid mass included between the two pelvic bones.
• The spines form a crest in the anterior third but are absent posteriorly.
• The transverse ridges on the ventral face indicate the positions of the transverse processes. The extremities of all the transverse processes fuse with the medial border of the ilium.