The vertebral column consists of five groups of vertebrae: cervical (C), thoracic (T), lumbar (L), sacral (S) and caudal (Cd) vertebrae. The vertebral formula for the dog is C7T13L7S3Cd20.
All typical vertebrae consist of a body, vertebral arch and three different processes. The body of a vertebra is convex cranially and concave caudally. Adjacent vertebral bodies are connected by intervertebral disks that composed of outer concentric layers of dense fibrocartilaginous tissue (anulus fibrosus) and inner soft center (nucleus pulposus). The vertebral arch is subdivided into right and left dorsl portion, the laminae, and ventral parts, the pedicles. The vertebral arch and the body form the vertebral foramen that all join to form a vertebral canal. Each typical vertebra has a single spinous process, paired transverse processes, and paired cranial and caudal articular processes.
Cervical Vertebrae: The chief peculiarities are modified articular processes, a reduced spinous process, and a reduction of its body.
Thoracic Vertebrae: The bodies of the thoracic vertebrae are short. The spine is the most conspicuous feature of each of the first nine thoracic vertebrae. The size of the spines gradually decreases with successive vertebrae moving distally but there is very little noticeable change in length and direction until the seventh or eight vertebrae is reached. The spine of the eleventh thoracic vertebra is almost perpendicular to the long axis of that bone. This vertebra is termed the anticlinal vertebra.
Lumbar Vertebrae: The lumbar vertebrae have longer bodies than the thoracic vertebrae. The transverse processes are directed cranially as well as ventrolaterally. Lying in a sagittal plane are they articular processes. The spinous processes are blunt and are to be found in the midlumbar region and have a slight cranial direction to them. The seventh lumbar vertebra is slightly shorter than the other lumbar vertebrae.
Clinical Correlation: Hemivertebra is a congential vertebral anamoly that may cause neurologic problem. They are wedge-shaped vertebrae that can cause a dorsal curverture (Kyphosis) or a lateral curverture (Scoliosis). In dogs hemivertebrae are most common in caudal and thoracic vertebrae. Affected breeds include Bulldog, Pugs, and Boston Terriers.