Vertebral Column

The vertebral column, also known as the backbone or spinal column, is the central supporting structure of the skeleton. In humans, it consists of 33 vertebrae (singular : vertebra) stacked to form a flexible column with a central canal for the spinal cord. The vertebrae are separated by discs of fibro cartilage but held together by ligaments. These intervertebral discs allow the vertebrae to move slightly . so that the vertebral column can Ben backward and forwards, as well as , side ways. spinal nerves leave the spinal cord through openings between adjacent vertebrae.

    A typical vertebra has 

• a neutral for the passage of the spinal cord;

• a neutral spine which projects upwards dorsally;

• two processes , known as transverse processes, which project from the sides of each vertebra;

• a centrum which is a solid piece of bone below the neural canal; and 

• smooth surfaces or facts at the front a d back which is for into the adjacent vertebrae.

    The first and second vertebrae of the column are the atlas and the axis respectively. They are  cervical vertebrae. The atlas is a ring of bone with a very large neural canal and no centrum. It has a pair of large hollow facets which fit into two bulging surfaces of the skull in a manner that permits nodding movements of the head. Unlike atlas , the axis has a large centrum which projects forward as the odontoid process. This fits into the ventral portion of the neural canal of the atlas is thus able to rotate on the axis , allowing the head to turn from side to side.

   The atlas , axis and the next five vertebrae make up the cervical vertebrae. The twelve thoracic vertebrae are attached to the ribs. The five lumbar vertebrae are massive and support most of the body weight. The five sacral vertebrae are fused to form a sacrum which articulates with the pelvic girdle. In humans, the four caudal vertebrae are fused to form the coccyx. In most other mammals, the caudal vertebrae are not fused. A rabbit has about sixteen caudal vertebrae, while a rat has between twenty seven to thirty caudal vertebrae.