The spinal column
, a defining
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
shared by nearly all vertebrates
[ Hagfish are believed to have secondarily lost their spinal column]
is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic irregular bone
whose complex structure is composed primarily of
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
, and secondarily of hyaline cartilage
. They show variation in the proportion contributed by these two tissue types; such variations correlate
on one hand with the cerebral/caudal rank
(i.e., location within the backbone
), and on the other with
In biology, phylogenetics (; from Greek φυλή/ φῦλον  "tribe, clan, race", and wikt:γενετικός, γενετικός  "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
differences among the vertebrate taxa
The basic configuration of a vertebra varies, but the bone is its ''body'', with the central part of the body constituting the ''centrum''. The upper (closer to) and lower (further from), respectively, the cranium and its
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all ...
surfaces of the vertebra body support attachment to the
An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to ho ...
s. The posterior part of a vertebra forms a vertebral arch (in eleven parts, consisting of
* two pedicles (pedicle of vertebral arch)
* two laminae, and
* seven processes
The laminae give attachment to the ligamenta flava
, which are ligaments of the spine. There are vertebral notches, each constituted by the shape of the pedicles, which form the intervertebral foramina
when vertebrae articulate
. These foramina are the entry and exit conduits accommodating the spinal nerve
s. The body of the vertebra, and its vertebral arch, form the vertebral foramen
, which is the larger, stable and central opening: this accommodates the spinal canal
, and encloses and protects the
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
Vertebrae articulate with each other to give strength and flexibility to the spinal column, and the shape at their back and front aspects determines the range of movement. Structurally, vertebrae are essentially alike across the vertebrate species, with the greatest difference seen between an aquatic animal
and other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column.
Structure in humans
In the human vertebral column
the size of the vertebrae varies according to placement in the vertebral column, spinal loading, posture and pathology. Along the length of the spine
the vertebrae change to accommodate different needs related to stress and mobility. Each vertebra is an irregular bone.
Every vertebra has a body (vertebral body), which consists of a large anterior middle portion called the centrum (vertebral centrum, plural ''centra'') and a posterior vertebral arch,
also called a neural arch. The body is composed of cancellous bone
, which is the spongy type of osseous tissue
, whose microanatomy has been specifically studied within the pedicle bones. This cancellous bone is in turn, covered by a thin coating of cortical bone
(or compact bone), the hard and dense type of osseous tissue. The vertebral arch and processes have thicker coverings of cortical bone. The upper and lower surfaces of the body of the vertebra are flattened and rough in order to give attachment to the intervertebral discs
. These surfaces are the vertebral endplates which are in direct contact with the intervertebral discs and form the joint. The endplates are formed from a thickened layer of the cancellous bone of the vertebral body, the top layer being more dense. The endplates function to contain the adjacent discs, to evenly spread the applied loads, and to provide anchorage for the collagen fibers
of the disc. They also act as a semi-permeable interface for the exchange of water and solutes.
The vertebral arch is formed by pedicles and laminae. Two pedicles extend from the sides of the vertebral body to join the body to the arch. The pedicles are short thick process
es that extend, one from each side, posteriorly, from the junctions of the posteriolateral surfaces of the centrum, on its upper surface.
From each pedicle a broad plate, a lamina, projects backwards and medialwards to join and complete the vertebral arch and form the posterior border of the vertebral foramen, which completes the triangle of the vertebral foramen.
The upper surfaces of the laminae are rough to give attachment to the ligamenta flava
. These ligaments connect the laminae of adjacent vertebra along the length of the spine from the level of the second cervical vertebra. Above and below the pedicles are shallow depressions called vertebral notches (''superior'' and ''inferior''). When the vertebrae articulate
the notches align with those on adjacent vertebrae and these form the openings of the intervertebral foramina
. The foramina allow the entry and exit of the spinal nerves from each vertebra, together with associated blood vessels. The articulating vertebrae provide a strong pillar of support for the body.
There are seven processes projecting from the vertebra:
* one spinous process
* two transverse processes
* four articular processes
A major part of a vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally.
This process points dorsally
from the junction of the laminae.
The spinous process serves to attach
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of ...
s and ligament
The two transverse processes, one on each side of the vertebral body, project laterally from either side at the point where the lamina joins the pedicle
, between the superior and inferior articular processes.
They also serve for the attachment of muscles and ligaments, in particular the intertransverse ligament
s. There is a facet on each of the transverse processes of thoracic vertebrae which articulates with the tubercle of the rib
. A facet on each side of the thoracic vertebral body articulates with the head of the rib
. The transverse process of a lumbar vertebra
is also sometimes called the ''costal''
[Platzer (2004), pp 42–43] [Latin ''costa'' refers to either a "rib" or "side" of the body. (Diab (1999), p 76)]
or ''costiform process''
[Tweedie, A. ''The library of medicine']
/ref> because it corresponds to a rudimentary rib (''costa'') which, as opposed to the thorax, is not developed in the lumbar region.
There are superior and inferior articular facet joints on each side of the vertebra, which serve to restrict the range of movement possible. These facets are joined by a thin portion of the vertebral arch called the '' pars interarticularis''.
Vertebrae take their names from the regions of the vertebral column that they occupy. There are thirty-three vertebrae in the human vertebral column—seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five fused sacral vertebrae forming the
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ... and three to five coccygeal vertebrae, forming the coccyx. The regional vertebrae increase in size as they progress downwards but become smaller in the coccyx.
There are seven cervical vertebrae (but eight cervical spinal nerves), designated C1 through C7. These bones are, in general, small and delicate. Their spinous processes are short (with the exception of C2 and C7, which have palpable spinous processes). C1 is also called the atlas, and C2 is also called the axis. The structure of these vertebrae is the reason why the
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ... and head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animal ... have a large range of motion. The atlanto-occipital joint allows the skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ... to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right. The axis also sits upon the first intervertebral disc of the spinal column.
Cervical vertebrae possess transverse foramina to allow for the vertebral arteries to pass through on their way to the foramen magnum to end in the circle of Willis. These are the smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and often bifurcated (the spinous process of C7, however, is not bifurcated, and is substantially longer than that of the other cervical spinous processes).
The atlas differs from the other vertebrae in that it has no body and no spinous process. It has instead a ring-like form, having an anterior and a posterior arch and two lateral masses. At the outside centre points of both arches there is a tubercle, an anterior tubercle and a posterior tubercle, for the attachment of muscles. The front surface of the anterior arch is convex and its anterior tubercle gives attachment to the longus colli muscle. The posterior tubercle is a rudimentary spinous process and gives attachment to the rectus capitis posterior minor muscle. The spinous process is small so as not to interfere with the movement between the atlas and the skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t .... On the under surface is a facet for articulation with the dens of the axis.
Specific to the cervical vertebra is the transverse foramen (also known as ''foramen transversarium''). This is an opening on each of the transverse processes which gives passage to the vertebral artery and vein
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ... and a sympathetic nerve plexus. On the cervical vertebrae other than the atlas, the anterior and posterior tubercles are on either side of the transverse foramen on each transverse process. The anterior tubercle on the sixth cervical vertebra is called the carotid tubercle because it separates the carotid artery Carotid artery may refer to:
* Common carotid artery, often "carotids" or "carotid", an artery on each side of the neck which divides into the external carotid artery and internal carotid artery
* External carotid artery, an artery on each side of ... from the vertebral artery.
There is a hook-shaped uncinate process on the side edges of the top surface of the bodies of the third to the seventh cervical vertebrae and of the first thoracic vertebra. Together with the vertebral disc, this uncinate process prevents a vertebra from sliding backwards off the vertebra below it and limits lateral flexion (side-bending). Luschka's joints involve the vertebral uncinate processes.
The spinous process on C7 is distinctively long and gives the name vertebra prominens to this vertebra. Also a cervical rib can develop from C7 as an anatomical variation.
The term cervicothoracic is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas.
The twelve thoracic vertebrae and their transverse processes have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much ''flexion'' or other movement. They may also be known as "dorsal vertebrae" in the human context.
The vertebral bodies are roughly heart-shaped and are about as wide anterio-posteriorly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape.
The top surface of the first thoracic vertebra has a hook-shaped uncinate process, just like the cervical vertebrae.
The thoracolumbar division refers to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas.
The thoracic vertebrae attach to ribs and so have articular facets specific to them; these are the superior, transverse and inferior costal facets. As the vertebrae progress down the spine they increase in size to match up with the adjoining lumbar section.
The five lumbar vertebrae are the largest of the vertebrae, their robust construction being necessary for supporting greater weight than the other vertebrae. They allow significant ''flexion'', ''extension'' and moderate lateral flexion (side-bending). The discs between these vertebrae create a natural lumbar lordosis (a spinal curvature that is concave posteriorly). This is due to the difference in thickness between the front and back parts of the intervertebral discs.
The lumbar vertebrae are located between the ribcage and the pelvis and are the largest of the vertebrae. The pedicles are strong, as are the laminae, and the spinous process is thick and broad. The vertebral foramen is large and triangular. The transverse processes are long and narrow and three tubercles can be seen on them. These are a lateral costiform process, a mammillary process and an accessory process.
[Postacchini, Franco (1999) ''Lumbar Disc Herniation']
/ref> The superior, or upper tubercle is the mammillary process which connects with the superior articular process. The multifidus muscle attaches to the mammillary process and this muscle extends through the length of the vertebral column, giving support. The inferior, or lower tubercle is the accessory process and this is found at the back part of the base of the transverse process. The term lumbosacral is often used to refer to the lumbar and sacral vertebrae together, and sometimes includes their surrounding areas.
There are five sacral vertebrae (S1–S5) which are fused in maturity, into one large bone, the
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ..., with no intervertebral disc
An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to ho ...s. The sacrum with the ilium forms a sacroiliac joint on each side of the pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ..., which articulates with the hips.
The last three to five coccygeal vertebrae (but usually four) (Co1–Co5) make up the tailbone or coccyx. There are no
An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to ho ...s.
Somites form in the early
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ... and some of these develop into sclerotomes. The sclerotomes form the vertebrae as well as the rib cartilage and part of the occipital bone
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the .... From their initial location within the somite, the sclerotome cells migrate medially towards the notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis .... These cells meet the sclerotome cells from the other side of the paraxial mesoderm
Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running .... The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body. [
Walker, Warren F., Jr. (1987) ''Functional Anatomy of the Vertebrate'' San Francisco: Saunders College Publishing.] From this vertebral body, sclerotome cells move dorsally and surround the developing spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ..., forming the vertebral arch. Other cells move distally to the costal processes of thoracic vertebrae to form the ribs.
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
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ... and covering meninges
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located .... 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
Spinal cord direv.svg, The spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ... nested in the vertebral column.
Gray298.png, Vertebral joint
Gray313.png, Costovertebral joint
Gray90.png, A facet joint between the superior and inferior articular processes (labeled at top and bottom).
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 is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not t ... 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
An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to ho ..., 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 stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture).
''Stricture' ..., a narrowing of the nerve opening, as a result of arthritis
Arthritis is a term often used to mean any disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, swelling, and decreased range of motion of the affected joints. In so ....
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.
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
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantid ... the vertebrae are connected by tight joints, which limit the backbone's flexibility. Spinous processes are exaggerated in some animals, such as the extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed an ... '' 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.
"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
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalian ..., but are found in some amphibians
Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arb ... such as frogs. The vertebrae fit together in a ball-and-socket articulation, in which the convex articular feature of an anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position p ... 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
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of ... 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 lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...s 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 mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...s except manatee
Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living specie ...s and sloth
Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their ...s 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
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ... 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 marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...s have thirteen, but koala
The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the ...s only have eleven. The norm is twelve to fifteen in mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...s, (twelve in the human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cult ...), though there are from eighteen to twenty in the horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 millio ..., tapir, rhinoceros
A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species ... and elephant
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantid .... 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 chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...s and gorillas, which have three in contrast to the five in the genus '' Homo
''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely rela ...''. 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 primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includ ...s, they are called the coccygeal vertebrae, number from three to five and are fused into the coccyx.
File:Gray303.png, Vertebral arches of three thoracic vertebrae
File:Gray312.png, Costovertebral joints seen from the front
File:Sobo 1909 9.png, Lower thoracic and upper lumbar vertebrae seen from the side
File:Sobo 1909 4.png, Cervical vertebrae seen from the back
File:Vertebrae Anatomy by Jason Christian.webm, Vertebrae Anatomy
* Limbus vertebra
* Functional spinal unit
* Pott disease
* Scheuermann's disease
* – Axis & Atlas Articulated, Posterior View
- BlueLink Anatomy - University of Michigan Medical School
– University of the Cumberlands