The first two cervical vertebrae, the atlas and axis, have a distinct morphology that reflects their more specialized function. There is no intervertebral disc between the atlas and axis. With the exception of C7, the vertebral arteries pass through transverse foramina in the transverse processes of the cervical vertebrae. The axis has a very large dorsal spinous process that extends over the atlas and is connected to it by the atlantoaxial ligament. The dens arises embryologically from the atlas and has a separate growth plate. It projects cranially from the body of the axis and lies on the floor of the vertebral canal. Thoracic vertebrae articulate with the ribs and have small vertebral bodies and large dorsal spinous process. Lumbar vertebrae have very long vertebral bodies with short
SURGICAL ANATOMY VERTEBRAE The vertebral column is composed of a series of 51-54 vertebrae, most of which are joined by intervertebral discs, ligaments, and the synovial joints between the articular processes. The basic structure of each vertebra is similar, although the morphology varies from one region of the spine to another. Each vertebra has a vertebral arch comprising two pedicles and a dorsal lamina. The vertebral canal is formed from the vertebral arch laterally and dorsally and the vertebral body ventrally. Most vertebrae have transverse processes projecting laterally from the vertebral body, a spinous process projecting dorsally from the lamina, and cranial and caudal articular processes on the vertebral arch. Other bony processes vary according to region. The synovial articulations lie dorsally except for those between the first and second cervical vertebrae (C1-2), where they are ventral, and the sacrum, where they are fused. These
spinous processes angled cranially. The lumbar transverse processes project cranioventrally, overlapping the preceding vertebra. The ventral deflection of these processes is more pronounced in the cat than the dog. The transverse processes are short on the first lumbar vertebra (L1) but become progressively narrower and longer on more caudal vertebrae. The ribs and the transverse processes of L1 at the thoracolumbar junction are important landmarks when performing surgery in this region of the spine. The three sacral vertebrae are fused to form one body, which articulates with the pelvis at the sacroiliac joints.