vertebrae somites form in the early embryo and some of these develop into sclerotomes. the sclerotomes form the vertebrae as well as the rib cartilage and part of the occipital bone. from their initial location within the somite, the sclerotome cells migrate medially towards the notochord. these cells meet the sclerotome cells from the other side of the paraxial mesoderm. the lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body. from this vertebral body, sclerotome cells move dorsally and surround the developing spinal cord, forming the vertebral arch. other cells move distally to the costal processes of thoracic vertebrae to form the ribs. function functions of vertebrae include: support of the vertebrae function in the skeletomuscular system by forming the vertebral column to support the body protection. vertebrae contain a vertebral foramen for the passage of the spinal canal and its enclosed spinal cord and covering meninges. they also afford sturdy protection for the spinal cord. the upper and lower surfaces of the centrum are flattened and rough in order to give attachment to the intervertebral discs. movement. the vertebrae also provide the openings, the intervertebral foramina which allow the entry and exit of the spinal nerves. similarly to the surfaces of the centrum, the upper and lower surfaces of the fronts of the laminae are flattened and rough to give attachment to the ligamenta flava. working together in the vertebral column their sections provide controlled movement and flexibility. feeding of the intervertebral discs through the reflex (hyaline ligament) plate that separates the cancellous bone of the vertebral body from each disk the spinal cord nested in the vertebral column vertebral joint costovertebral joint a facet joint between the superior and inferior articular processes (labeled at top and bottom) clinical significance there are a number of congenital vertebral anomalies, mostly involving variations in the shape or number of vertebrae, and many of which are unproblematic. others though can cause compression of the spinal cord. wedge-shaped vertebrae, called hemivertebrae can cause an angle to form in the spine which can result in the spinal curvature diseases of kyphosis, scoliosis and lordosis. severe cases can cause spinal cord compression. block vertebrae where some vertebrae have become fused can cause problems. spina bifida can result from the incomplete formation of the vertebral arch. spondylolysis is a defect in the pars interarticularis of the vertebral arch. in most cases this occurs in the lowest of the lumbar vertebrae (l5), but may also occur in the other lumbar vertebrae, as well as in the thoracic vertebrae. spinal disc herniation, more commonly called a slipped disc, is the result of a tear in the outer ring (anulus fibrosus) of the intervertebral disc, which lets some of the soft gel-like material, the nucleus pulposus, bulge out in a hernia. this may be treated by a minimally-invasive endoscopic procedure called tessys method. a laminectomy is a surgical operation to remove the laminae in order to access the spinal canal. the removal of just part of a lamina is called a laminotomy. a pinched nerve caused by pressure from a disc, vertebra or scar tissue might be remedied by a foraminotomy to broaden the intervertebral foramina and relieve pressure. it can also be caused by a foramina stenosis, a narrowing of the nerve opening, as a result of arthritis. another condition is spondylolisthesis when one vertebra slips forward onto another. the reverse of this condition is retrolisthesis where one vertebra slips backwards onto another. the vertebral pedicle is often used as a radiographic marker and entry point in vertebroplasty, kyphoplasty, and spinal fusion procedures. the arcuate foramen is a common anatomical variation more frequently seen in females. it is a bony bridge found on the first cervical vertebra, the atlas where it covers the groove for the vertebral artery. degenerative disc disease is a condition usually associated with ageing in which one or more discs degenerate. this can often be a painfree condition but can also be very painful. other animals regions of vertebrae in the goat in other animals the vertebrae take the same regional names except for the coccygeal; in animals with tails the separate vertebrae are usually called the caudal vertebrae. because of the different types of locomotion and support needed between the aquatic and other vertebrates, the vertebrae between them show the most variation, though basic features are shared. the spinous processes which are backward extending are directed upwards in animals without an erect stance. these processes can be very large in the larger animals since they attach to the muscles and ligaments of the body. in the elephant the vertebrae are connected by tight joints, which limit the backbone's flexibility. spinous processes are exaggerated in some animals, such as the extinct dimetrodon and spinosaurus, where they form a sailback or finback. vertebrae with saddle-shaped articular surfaces on their bodies, called "heterocoelous", allow vertebrae to flex both vertically and horizontally while preventing twisting motions. such vertebrae are found in the necks of birds and some turtles. an example of procoelous vertebrae dissected from a rattlesnake "procoelous" vertebrae feature a spherical protrusion extending from the caudal end of the centrum of one vertebra that fits into a concave socket on the cranial end of the centrum of an adjacent vertebra. these vertebrae are most often found in reptiles, but are found in some amphibians such as frogs. the vertebrae fit together in a ball-and-socket articulation, in which the convex articular feature of an anterior vertebra acts as the ball to the socket of a caudal vertebra. this type of connection permits a wide range of motion in most directions, while still protecting the underlying nerve cord. the central point of rotation is located at the midline of each centrum, and therefore flexion of the muscle surrounding the vertebral column does not lead to an opening between vertebrae. in many species, though not in mammals, the cervical vertebrae bear ribs. in many groups, such as lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. the transverse processes of mammals are homologous to the cervical ribs of other amniotes. in the whale the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming. all mammals except manatees and sloths have seven cervical vertebrae, whatever the length of the neck. this includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example. birds usually have more cervical vertebrae with most having a highly flexible neck consisting of 13–25 vertebrae. in all mammals, the thoracic vertebrae are connected to ribs and their bodies differ from the other regional vertebrae due to the presence of facets. each vertebra has a facet on each side of the vertebral body, which articulates with the head of a rib. there is also a facet on each of the transverse processes which articulates with the tubercle of a rib. the number of thoracic vertebrae varies considerably across the species. most marsupials have thirteen, but koalas only have eleven. the norm is twelve to fifteen in mammals, (twelve in the human), though there are from eighteen to twenty in the horse, tapir, rhinoceros and elephant. in certain sloths there is an extreme number of twenty-five and at the other end only nine in the cetacean. there are fewer lumbar vertebrae in chimpanzees and gorillas, which have three in contrast to the five in the genus homo. this reduction in number gives an inability of the lumbar spine to lordose but gives an anatomy that favours vertical climbing, and hanging ability more suited to feeding locations in high-canopied regions. the bonobo differs by having four lumbar vertebrae. caudal vertebrae are the bones that make up the tails of vertebrates. they range in number from a few to fifty, depending on the length of the animal's tail. in humans and other tailless primates, they are called the coccygeal vertebrae, number from three to five and are fused into the coccyx. additional images vertebral arches of three thoracic vertebrae costovertebral joints seen from the front lower thoracic and upper lumbar vertebrae seen from the side cervical vertebrae seen from the back