Axial Structures

Vertebral Formulae

• Vertebral formulae for different animals: • Dogs: C7, T13, L7, S3 • Cats: C7, T13, L7, S3 • Ox (cows): C7, T13, L6, S5 • Horses (and donkeys): C7, T18, L6, S5
• All animals have C7, except horses with T18
• Small animals (dogs and cats) have L7 and S3
• Large animals (Ox and horses) have L6 and S5

Vertebral Features

• Vertebral body: • Intervertebral discs are located between the bodies of each vertebra
• Vertebral arch: • Consists of paired pedicles (sides) and paired laminae (roof) • Vertebral foramina are surrounded by the arch and dorsal surface of the body
• Processes: • (Dorsal) spinous process • Transverse process: bilateral • Articular process: cranial and caudal pairs
• Synovial joint

Vertebral Canal and Intervertebral Foramina

• Vertebral canal: • Formed by the vertebral foramina and houses the spine
• Intervertebral foramina: • Located laterally between adjacent vertebrae, formed by vertebral notches • Spinal nerves and blood vessels course through this

Cervical Vertebrae: General Info

• Transverse foramina present in C1-C6 vertebrae
• Atlanto-occipital joint: • Located between atlas and occipital condyles of the skull • Allows for extension and flexion only (referred to as the "yes" joint) • Can be used for CSF (cerebral spinal fluid) sampling
• Atlantoaxial joint: • Located between C1 and C2, allows for rotational movement (referred to as the "no" joint)
• Transverse ligament of the atlas: • Courses across the vertebral arch of C1, holding the dens against the atlas
• Apical ligament of the dens: • Runs from the dens of the axis to the occipital bone of the skull
• Alar ligament: • Runs from the dens of the axis to the occipital bone of the skull
• C1-C6 have transverse foramina for vertebral veins, arteries, and nerves
• C6 has an expanded ventral transverse process
• C7 lacks a transverse foramina and caudal costal foveae

Cervical Vertebrae: Atlas

• Atlas (C1 vertebrae): • Has no spinous process • Articulates with the occipital condyles of the skull • Has transverse foramina for vertebral artery, vein, and nerve

Cervical Vertebrae: Axis

• Axis (C2 vertebrae): • Has a large elongated spinous process • Dens (peg-like eminence) articulates with the atlas • Dens lies inside the vertebral canal, ventral to the spinal cord • Dens can indicate the cranial aspect of the bone

Thoracic Vertebrae

• Cranial thoracic vertebrae: • Have tall spinous processes and short transverse processes
• T11 (anticlinal vertebra): • Has a spinous process perpendicular to the body (T16 in horses)
• Thoracic vertebrae: • Have costal fovea present on vertebral bodies and transverse processes for rib articulation • Have extra processes for muscle attachment

Rib Articulation

• All 13 ribs: • The tubercle of the rib articulates with the transverse process of the same numbered vertebra • The head of the rib articulates with the body of the same numbered vertebra
• Ribs 1-20: • The head of the rib articulates with the body of the preceding vertebrae too

Costovertebral Ligaments

• Intercapital ligaments: • Extend across the dorsal surface of the intervertebral disk, holding heads of ribs in place • Reinforce the dorsal walls of intervertebral discs, making them less likely to herniate
• Costotransverse ligaments: • Course between the ribs and transverse process of the vertebra

Ribs and Sternum

• Ribs: • Have a bony and cartilaginous part (costochondral junction) • Dogs and cats have 13 pairs of ribs • Ribs 1-9 are "true ribs" that connect to the sternum • Ribs 10-12 articulate with the cartilage of cranial rib to form the costal arch • Rib 13 is the "floating rib"
• Sternum: • Composed of 8 sternebrae • Manubrium is the 1st sternebra • Xiphoid process is the last sternebra

Lumbar Vertebrae

• Lumbar vertebrae: • Have large bodies and a large transverse process that points cranially • Have a prominent spinous process, mammillary processes (on either side of spinous process), and accessory processes that point caudally

Sacrum

• Sacrum: • Composed of fused S1, S2, and S3 vertebrae • Has a median sacral crest formed by the fused spinous processes • Has fused transverse processes • Articulates with the ilium • Uses dorsal and pelvic sacral foramina instead of intervertebral foramina for spinal nerves

Caudal/Coccygeal Vertebrae

• Caudal/coccygeal vertebrae: • Can be abbreviated to "Cd" or "Ca", while "C" is strictly used for cervical vertebrae • The first few caudal vertebrae look like typical vertebrae, then become more rod-shaped • Hemal arch is located on Cd4-Cd6, protecting tail vessels

Intervertebral Disc

• Intervertebral disc: • Located between vertebral bodies, except for C1-C2 and at the sacrum • Composed of a fibrocartilaginous structure with 2 parts: anulus fibrosus and nucleus pulposus • Works as a shock absorber, spreading the load evenly between the bones

Vertebral Ligaments

• Supraspinous ligament: • Courses dorsally along the spinous processes of the T1-Cd3 vertebrae
• Nuchal ligament: • A cranial extension of the supraspinous ligament • In dogs, courses between the spinous processes of the axis (C2) and T1 • In large animals, attaches to the skull, rather than C2 • Cats and pigs lack nuchal ligaments