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73-579: Espinal , Spanish for spine , may refer to: People [ edit ] Espinal (surname) Places [ edit ] Argentine Espinal , an ecoregion in Argentina Espinal, Navarre , Spain Espinal, Veracruz , Mexico El Espinal, Oaxaca , Mexico El Espinal, Tolima , Colombia Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

146-628: A hernia . Spinal stenosis is a narrowing of the spinal canal which can occur in any region of the spine though less commonly in the thoracic region. The stenosis can constrict the spinal canal giving rise to a neurological deficit . Pain at the coccyx (tailbone) is known as coccydynia . Spinal cord injury is damage to the spinal cord that causes changes in its function, either temporary or permanent. Spinal cord injuries can be divided into categories: complete transection, hemisection, central spinal cord lesions, posterior spinal cord lesions, and anterior spinal cord lesions. Scalloping vertebrae

219-412: A central cavity, the central canal . Adjacent to each vertebra emerge spinal nerves . The spinal nerves provide sympathetic nervous supply to the body, with nerves emerging forming the sympathetic trunk and the splanchnic nerves . The spinal canal follows the different curves of the column; it is large and triangular in those parts of the column that enjoy the greatest freedom of movement, such as

292-449: A curve, convex forward, that begins at the axis (second cervical vertebra) at the apex of the odontoid process or dens and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. This inward curve is known as a lordotic curve. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to

365-413: A neural arch, while the haemal arch is found underneath the centrum in the caudal (tail) vertebrae of fish , most reptiles , some birds, some dinosaurs and some mammals with long tails. The vertebral processes can either give the structure rigidity, help them articulate with ribs, or serve as muscle attachment points. Common types are transverse process, diapophyses, parapophyses, and zygapophyses (both

438-535: A region can vary but overall the number remains the same. In a human vertebral column, there are normally 33 vertebrae. The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs , and the lower nine are fused in adults, five in the sacrum and four in the coccyx , or tailbone . The articulating vertebrae are named according to their region of the spine. From top to bottom, there are 7 cervical vertebrae , 12 thoracic vertebrae and 5 lumbar vertebrae . The number of those in

511-456: A region can vary but overall the number remains the same. The number of those in the cervical region, however, is only rarely changed. The vertebrae of the cervical, thoracic, and lumbar spines are independent bones and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis , on which the head rests. A typical vertebra consists of two parts:

584-399: A remnant of the notochord. Reptiles often retain the primitive intercentra, which are present as small crescent-shaped bony elements lying between the bodies of adjacent vertebrae; similar structures are often found in the caudal vertebrae of mammals. In the tail, these are attached to chevron-shaped bones called haemal arches , which attach below the base of the spine, and help to support

657-438: A result of lifting the head and the lumbar curvature forms as a result of walking. The vertebral column surrounds the spinal cord which travels within the spinal canal , formed from a central hole within each vertebra . The spinal cord is part of the central nervous system that supplies nerves and receives information from the peripheral nervous system within the body. The spinal cord consists of grey and white matter and

730-423: A rough, uneven border, thickest below where it is occasionally notched. The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets on the superior processes are concave, and look backward and medialward ; those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than

803-468: A single segment is difficult to measure clinically, not only because of variations between individuals, but also because it is age and sex dependent. Furthermore, flexion and extension in the lumbal spine is the product of a combination of rotation and translation in the sagittal plane between each vertebra. Ranges of segmental movements in the lumbar spine (White and Punjabi, 1990) are (in degrees): Congenital vertebral anomalies can cause compression of

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876-504: A vertebral column. The human spine is one of the most-studied examples, as the general structure of human vertebrae is fairly typical ( homologous ) of that found in other mammals , reptiles and birds . The shape of the vertebral body does, however, vary somewhat between different groups of living species. Individual vertebrae are named according to their corresponding body region ( neck , thorax , abdomen , pelvis or tail ). In clinical medicine , features on vertebrae (particularly

949-465: Is assumed that the chimpanzee–human last common ancestor also had a long vertebral column with a long lumbar region and that the reduction in the number of lumbar vertebrae evolved independently in each ape clade . The limited number of lumbar vertebrae in chimpanzees and gorillas result in an inability to lordose (curve) their lumbar spines, in contrast to the spines of Old World monkeys and Nacholapithecus and Proconsul , which suggests that

1022-660: Is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacrovertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes, and by the thickness of its transverse processes, which spring from the body as well as from the pedicles. The fifth lumbar vertebra is by far the most common site of spondylolysis and spondylolisthesis . Most individuals have five lumbar vertebrae, while some have four or six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these latter individuals. The range of segmental movements in

1095-413: Is classed as a spinal disease or dorsopathy and includes the following abnormal curvatures: Individual vertebrae of the human vertebral column can be felt and used as surface anatomy , with reference points are taken from the middle of the vertebral body. This provides anatomical landmarks that can be used to guide procedures such as a lumbar puncture and also as vertical reference points to describe

1168-416: Is curved in several places, a result of human bipedal evolution . These curves increase the vertebral column's strength, flexibility, and ability to absorb shock, stabilising the body in upright position. When the load on the spine is increased, the curvatures increase in depth (become more curved) to accommodate the extra weight. They then spring back when the weight is removed. The upper cervical spine has

1241-437: Is kidney shaped, wider from side to side than from front to back, and a little thicker in front than in back. It is flattened or slightly concave above and below, concave behind, and deeply constricted in front and at the sides. The pedicles are very strong, directed backward from the upper part of the vertebral body; consequently, the inferior vertebral notches are of considerable depth. The pedicles change in morphology from

1314-412: Is lateral, the mammillary is superior (cranial), and the accessory is inferior (caudal). The mammillary is connected in the lumbar region with the back part of the superior articular process. The accessory process is situated at the back part of the base of the transverse process. The tallest and thickest costiform process is usually that of L5. The first lumbar vertebra is level with the anterior end of

1387-432: Is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the spinous processes are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In

1460-412: Is the increase in the concavity of the posterior vertebral body. It can be seen on lateral X-ray and sagittal views of CT and MRI scans. Its concavity is due to the increased pressure exerting on the vertebrae due to a mass. Internal spinal mass such as spinal astrocytoma , ependymoma , schwannoma , neurofibroma , and achondroplasia causes vertebrae scalloping. Excessive or abnormal spinal curvature

1533-521: The Arabian (breed) can have one less vertebrae and pair of ribs. This anomaly disappears in foals that are the product of an Arabian and another breed of horse. Vertebrae are defined by their location in the vertebral column. Cervical vertebrae are those in the neck area. With the exception of the two sloth genera ( Choloepus and Bradypus ) and the manatee genus, ( Trichechus ), all mammals have seven cervical vertebrae. In other vertebrates,

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1606-433: The intervertebral discs . The notochord disappears in the sclerotome (vertebral body) segments but persists in the region of the intervertebral discs as the nucleus pulposus . The nucleus pulposus and the fibers of the anulus fibrosus make up the intervertebral disc. The primary curves (thoracic and sacral curvatures) form during fetal development. The secondary curves develop after birth. The cervical curvature forms as

1679-428: The ninth rib . This level is also called the important transpyloric plane , since the pylorus of the stomach is at this level. Other important structures are also located at this level, they include; fundus of the gall bladder, celiac trunk, superior mesenteric artery, termination of spinal cord, beginning of filum terminale , renal vessels, middle suprarenal arteries, and hila of kidneys . The fifth lumbar vertebra

1752-412: The paraxial mesoderm that lies at the sides of the neural tube and they contain the precursors of spinal bone, the vertebrae ribs and some of the skull, as well as muscle, ligaments and skin. Somitogenesis and the subsequent distribution of somites is controlled by a clock and wavefront model acting in cells of the paraxial mesoderm. Soon after their formation, sclerotomes , which give rise to some of

1825-436: The sacrum and coccyx are fused without a central foramen. The vertebral arch is formed by a ventral pair of pedicles and a dorsal pair of laminae , and supports seven processes , four articular , two transverse and one spinous , the latter also being known as the neural spine. The transverse and spinous processes and their associated ligaments serve as important attachment sites for back and paraspinal muscles and

1898-435: The spinal canal , a body cavity that contains the spinal cord . Because the vertebral column will outgrow the spinal cord during child development , by adulthood the spinal cord often ends at the upper lumbar spine (at around L1/L2 level), the lower ( caudal ) end of the spinal canal is occupied by a ponytail -like bundle of spinal nerves descriptively called cauda equina (from Latin " horse's tail " ), and

1971-411: The spinal cord and the notochord . This column of tissue has a segmented appearance, with alternating areas of dense and less dense areas. As the sclerotome develops, it condenses further eventually developing into the vertebral body . Development of the appropriate shapes of the vertebral bodies is regulated by HOX genes . The less dense tissue that separates the sclerotome segments develop into

2044-427: The spinal cord by deforming the vertebral canal or causing instability. African apes have three and four lumbar vertebrae, ( bonobos have longer spines with an additional vertebra) and humans normally five. This difference, and because the lumbar spines of the extinct Nacholapithecus (a Miocene hominoid with six lumbar vertebrae and no tail) are similar to those of early Australopithecus and early Homo , it

2117-420: The spinous process ) can be used as surface landmarks to guide medical procedures such as lumbar punctures and spinal anesthesia . There are also many different spinal diseases in humans that can affect both the bony vertebrae and the intervertebral discs, with kyphosis / scoliosis , ankylosing spondylitis , degenerative discs and spina bifida being recognizable examples. The number of vertebrae in

2190-438: The thoracolumbar fasciae . The spinous processes of the cervical and lumbar regions can be felt through the skin, and are important surface landmarks in clinical medicine . The four articular processes for two pairs of plane facet joints above and below each vertebra, articulating with those of the adjacent vertebrae and are joined by a thin portion of the neural arch called the pars interarticularis . The orientation of

2263-409: The vertebral body (or centrum ), which is ventral (or anterior , in the standard anatomical position ) and withstands axial structural load ; and the vertebral arch (also known as neural arch ), which is dorsal (or posterior ) and provides articulations and anchorages for ribs and core skeletal muscles . Together, these enclose the vertebral foramen , the series of which align to form

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2336-411: The absence of the foramen transversarium within the transverse process (since it is only found in the cervical region ) and by the absence of facets on the sides of the body (as found only in the thoracic region ). They are designated L1 to L5, starting at the top. The lumbar vertebrae help support the weight of the body, and permit movement. The adjacent figure depicts the general characteristics of

2409-425: The adjacent vertebra to a degree less than a dislocation. Spondylolysis , also known as a pars defect, is a defect or fracture at the pars interarticularis of the vertebral arch. 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

2482-425: The back in quadrupeds . In humans, there are five lumbar vertebrae. The term is used to describe the anatomy of humans and quadrupeds, such as horses, pigs, or cattle. These bones are found in particular cuts of meat, including tenderloin or sirloin steak. In human anatomy, the five vertebrae are between the rib cage and the pelvis . They are the largest segments of the vertebral column and are characterized by

2555-416: The bone of the skull, the vertebrae and ribs, migrate, leaving the remainder of the somite now termed a dermamyotome behind. This then splits to give the myotomes which will form the muscles and dermatomes which will form the skin of the back. Sclerotomes become subdivided into an anterior and a posterior compartment. This subdivision plays a key role in the definitive patterning of vertebrae that form when

2628-427: The bony vertebral body. In most ray-finned fishes , including all teleosts , these two structures are fused with, and embedded within, a solid piece of bone superficially resembling the vertebral body of mammals. In living amphibians , there is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods. In cartilaginous fish , such as sharks ,

2701-506: The centrum. Centra with flat ends are acoelous , like those in mammals. These flat ends of the centra are especially good at supporting and distributing compressive forces. Amphicoelous vertebra have centra with both ends concave. This shape is common in fish, where most motion is limited. Amphicoelous centra often are integrated with a full notochord . Procoelous vertebrae are anteriorly concave and posteriorly convex. They are found in frogs and modern reptiles. Opisthocoelous vertebrae are

2774-423: The cervical and lumbar regions, and is small and rounded in the thoracic region, where motion is more limited. The spinal cord terminates in the conus medullaris and cauda equina . Spina bifida is a congenital disorder in which there is a defective closure of the vertebral arch. Sometimes the spinal meninges and also the spinal cord can protrude through this, and this is called spina bifida cystica . Where

2847-464: The cervical and upper part of the thoracic regions and gradually increasing in size to the last lumbar. They transmit the special spinal nerves and are situated between the transverse processes in the cervical region and in front of them, in the thoracic and lumbar regions. There are different ligaments involved in the holding together of the vertebrae in the column, and in the column's movement. The anterior and posterior longitudinal ligaments extend

2920-511: The cervical region, however, is only rarely changed, while that in the coccygeal region varies most. Excluding rare deviations, the total number of vertebrae ranges from 32 to 35. In about 10% of people, both the total number of pre-sacral vertebrae and the number of vertebrae in individual parts of the spine can vary. The most frequent deviations are: 11 (rarely 13) thoracic vertebrae, 4 or 6 lumbar vertebrae, 3 or 5 coccygeal vertebrae (rarely up to 7). There are numerous ligaments extending

2993-430: The cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina. The sides of the vertebral column are separated from

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3066-421: The child begins to walk. When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae. Below this, there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx. From behind,

3139-429: The condition does not involve this protrusion it is known as spina bifida occulta . Sometimes all of the vertebral arches may remain incomplete. Another, though rare, congenital disease is Klippel–Feil syndrome , which is the fusion of any two of the cervical vertebrae. Spondylolisthesis is the forward displacement of a vertebra and retrolisthesis is a posterior displacement of one vertebral body with respect to

3212-402: The cranial zygapophyses and the caudal zygapophyses). The centrum of the vertebra can be classified based on the fusion of its elements. In temnospondyls , bones such as the spinous process , the pleurocentrum and the intercentrum are separate ossifications. Fused elements, however, classify a vertebra as having holospondyly. A vertebra can also be described in terms of the shape of the ends of

3285-403: The curvatures of the vertebral column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are essentially alike, with minor variation. These regions are called the cervical spine, thoracic spine, lumbar spine, sacrum, and coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae. The number of vertebrae in

3358-447: The facet joints restricts the range of motion between the vertebrae. Underneath each pedicle is a small hole (enclosed by the pedicle of the vertebral below) called intervertebral foramen , which transmit the corresponding spinal nerve and dorsal root ganglion that exit the spinal canal. From top to bottom, the vertebrae are: For some medical purposes, adjacent vertebral regions may be considered together: The vertebral column

3431-426: The first through fourth lumbar vertebrae. The fifth vertebra contains certain peculiarities, which are detailed below. As with other vertebrae, each lumbar vertebra consists of a vertebral body and a vertebral arch . The vertebral arch, consisting of a pair of pedicles and a pair of laminae , encloses the vertebral foramen (opening) and supports seven processes . The vertebral body of each lumbar vertebra

3504-450: The latter since in the articulated column, the inferior articular processes are embraced by the superior processes of the subjacent vertebra. The transverse processes are long and slender. They are horizontal in the upper three lumbar vertebrae and incline a little upward in the lower two. In the upper three vertebrae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from

3577-449: The length of the column, which include the anterior and posterior longitudinal ligaments at the front and back of the vertebral bodies , the ligamentum flavum in deep to the laminae , the interspinous and supraspinous ligaments between spinous processes , and the intertransverse ligaments between the transverse processes . The vertebrae in the human vertebral column is divided into different body regions , which correspond to

3650-432: The length of the vertebral column along the front and back of the vertebral bodies. The interspinous ligaments connect the adjoining spinous processes of the vertebrae. The supraspinous ligament extends the length of the spine running along the back of the spinous processes, from the sacrum to the seventh cervical vertebra . From there it is continuous with the nuchal ligament . The striking segmented pattern of

3723-403: The locations of other parts of human anatomy, such as the positions of organs . The general structure of vertebrae in other animals is largely the same as in humans. Individual vertebrae are composed of a centrum (body), arches protruding from the top and bottom of the centrum, and various processes projecting from the centrum and/or arches. An arch extending from the top of the centrum is called

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3796-408: The lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line — which can sometimes be indicative of a fracture or a displacement of the spine. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it

3869-405: The mechanisms involved in vertebral segmentation are conserved across vertebrates. In humans the first four somites are incorporated in the base of the occipital bone of the skull and the next 33 somites will form the vertebrae, ribs, muscles, ligaments and skin. The remaining posterior somites degenerate. During the fourth week of embryogenesis , the sclerotomes shift their position to surround

3942-413: The musculature. These latter bones are probably homologous with the ventral ribs of fish. The number of vertebrae in the spines of reptiles is highly variable, and may be several hundred in some species of snake . Lumbar vertebrae The lumbar vertebrae are located between the thoracic vertebrae and pelvis . They form the lower part of the human back in humans, and the tail end of

4015-423: The next vertebral body fits. Even these patterns are only generalisations, however, and there may be variation in form of the vertebrae along the length of the spine even within a single species. Some unusual variations include the saddle-shaped sockets between the cervical vertebrae of birds and the presence of a narrow hollow canal running down the centre of the vertebral bodies of geckos and tuataras , containing

4088-405: The number of cervical vertebrae can range from a single vertebra in amphibians to as many as 25 in swans or 76 in the extinct plesiosaur Elasmosaurus . The dorsal vertebrae range from the bottom of the neck to the top of the pelvis . Dorsal vertebrae attached to the ribs are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. The sacral vertebrae are those in

4161-446: The opposite, possessing anterior convexity and posterior concavity. They are found in salamanders, and in some non-avian dinosaurs. Heterocoelous vertebrae have saddle -shaped articular surfaces. This type of configuration is seen in turtles that retract their necks, and birds, because it permits extensive lateral and vertical flexion motion without stretching the nerve cord too extensively or wringing it about its long axis. In horses,

4234-407: The pedicles and posterior parts of the vertebral bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs. Three portions or tubercles can be noticed in a transverse process of a lower lumbar vertebrae: the lateral or costiform process , the mammillary process , and the accessory process . The costiform

4307-423: The pelvic region, and range from one in amphibians, to two in most birds and modern reptiles, or up to three to five in mammals. When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. The synsacrum is a similar fused structure found in birds that is composed of the sacral, lumbar, and some of the thoracic and caudal vertebra, as well as the pelvic girdle . Caudal vertebrae compose

4380-418: The posterior part of one somite fuses to the anterior part of the consecutive somite during a process termed resegmentation. Disruption of the somitogenesis process in humans results in diseases such as congenital scoliosis. So far, the human homologues of three genes associated to the mouse segmentation clock, (MESP2, DLL3 and LFNG), have been shown to be mutated in cases of congenital scoliosis, suggesting that

4453-469: The posterior portion of the vertebral arch. In the upper lumbar region the lamina are taller than wide but in the lower lumbar vertebra the lamina are wider than tall. The lamina connects the spinous process to the pedicles. The vertebral foramen within the arch is triangular, larger than the thoracic vertebrae , but smaller than in the cervical vertebrae . The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in

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4526-417: The posterior surface by the articular processes in the cervical and thoracic regions and by the transverse processes in the lumbar region. In the thoracic region, the sides of the bodies of the vertebrae are marked in the back by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in

4599-542: The sacrovertebral articulation, and ends at the point of the coccyx ; its concavity is directed downward and forward as a kyphotic curve. The thoracic and sacral kyphotic curves are termed primary curves, because they are present in the fetus . The cervical and lumbar curves are compensatory , or secondary , and are developed after birth. The cervical curve forms when the infant is able to hold up its head (at three or four months) and sit upright (at nine months). The lumbar curve forms later from twelve to eighteen months, when

4672-401: The spine is established during embryogenesis when somites are rhythmically added to the posterior of the embryo. Somite formation begins around the third week when the embryo begins gastrulation and continues until all somites are formed. Their number varies between species: there are 42 to 44 somites in the human embryo and around 52 in the chick embryo. The somites are spheres, formed from

4745-446: The spinous process of the seventh thoracic vertebra. This curve is known as a kyphotic curve. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. This curve is described as a lordotic curve. The sacral curve begins at

4818-416: The tail, and the final few can be fused into the pygostyle in birds, or into the coccygeal or tail bone in chimpanzees (and humans ). The vertebrae of lobe-finned fishes consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects

4891-415: The tail. The general structure of human vertebrae is fairly typical of that found in other mammals , reptiles , and birds ( amniotes ). The shape of the vertebral body does, however, vary somewhat between different groups. In humans and other mammals, it typically has flat upper and lower surfaces, while in reptiles the anterior surface commonly has a concave socket into which the expanded convex face of

4964-540: The title Espinal . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Espinal&oldid=879849608 " Categories : Disambiguation pages Place name disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Vertebral column There are around 50,000 species of animals that have

5037-440: The upper lumbar to the lower lumbar. They increase in sagittal width from 9 mm to up to 18 mm at L5. They increase in angulation in the axial plane from 10 degrees to 20 degrees by L5. The pedicle is sometimes used as a portal of entrance into the vertebral body for fixation with pedicle screws or for placement of bone cement as with kyphoplasty or vertebroplasty. The laminae are broad, short, and strong. They form

5110-463: The upper surface of the notochord , and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in the primitive Labyrinthodonts , but in the evolutionary line that led to reptiles (and hence, also to mammals and birds), the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became

5183-449: The vertebrae consist of two cartilaginous tubes. The upper tube is formed from the vertebral arches, but also includes additional cartilaginous structures filling in the gaps between the vertebrae, and so enclosing the spinal cord in an essentially continuous sheath. The lower tube surrounds the notochord, and has a complex structure, often including multiple layers of calcification . Lampreys have vertebral arches, but nothing resembling

5256-409: The vertebral bodies found in all higher vertebrates . Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in the tail region. Hagfishes lack a true vertebral column, and are therefore not properly considered vertebrates, but a few tiny neural arches are present in

5329-475: The vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae), these are short, horizontal, and bifid. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in

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