Wikipedia

Vertebra

(Redirected fromLamina of the vertebral arch)
For other uses, seeVertebra (disambiguation).

Eachvertebra(pl.:vertebrae) is anirregular bonewith a complex structure composed ofboneand somehyaline cartilage,that make up thevertebral columnor spine, ofvertebrates.The proportions of the vertebrae differ according to their spinal segment and the particular species.

Vertebra
A typical vertebra, superior view
A section of thehuman vertebral column,showing multiple vertebrae in a left posterolateral view.
Details
Part ofSpinal column
Identifiers
Latinvertebra
TA98A02.2.01.001
TA21011
FMA9914
Anatomical terms of bone

The basic configuration of a vertebra varies; the bone is the body, and the central part of the body is the centrum. The upper and lower surfaces of the vertebra body give attachment to theintervertebral discs.The posterior part of a vertebra forms avertebral arch,in eleven parts, consisting of two pedicles (pedicle of vertebral arch), two laminae, and sevenprocesses.The laminae give attachment to theligamenta flava(ligaments of the spine). There are vertebral notches formed from the shape of the pedicles, which form theintervertebral foraminawhen the vertebraearticulate.These foramina are the entry and exit conduits for thespinal nerves.The body of the vertebra and the vertebral arch form the vertebral foramen, the larger, central opening that accommodates thespinal canal,which encloses and protects thespinal cord.

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 anaquatic animaland other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column.

Structure

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In the humanvertebral column,the size of the vertebrae varies according to placement in the vertebral column, spinal loading, posture and pathology. Along the length of thespine,the vertebrae change to accommodate different needs related to stress and mobility.[1]Each vertebra is an irregular bone.

Side view of vertebrae

A typical vertebra has abody(vertebral body), which consists of a large anterior middle portion called thecentrum(vertebral centrum,pluralcentra) and a posteriorvertebral arch,[2]also called aneural arch.[3]The body is composed ofcancellous bone,which is the spongy type ofosseous tissue,whose microanatomy has been specifically studied within the pedicle bones.[4]This cancellous bone is in turn, covered by a thin coating ofcortical 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 theintervertebral discs.These surfaces are the vertebralendplateswhich 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 thecollagen fibersof the disc. They also act as a semi-permeable interface for the exchange of water and solutes.[5]

Anatomy of a vertebra

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 thickprocessesthat 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, alamina,projects backward and medially to join and complete the vertebral arch and form the posterior border of the vertebral foramen, which completes the triangle of the vertebral foramen.[6]The upper surfaces of the laminae are rough to give attachment to theligamenta flava.These ligaments connect the laminae of adjacent vertebra along the length of the spine from the level of thesecond cervical vertebra.Above and below the pedicles are shallow depressions calledvertebral notches(superiorandinferior). When the vertebraearticulatethe notches align with those on adjacent vertebrae and these form the openings of theintervertebral 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.

Processes

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There are seven processes projecting from the vertebra:

A major part of a vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally.[7]This process pointsdorsallyandcaudallyfrom the junction of the laminae.[7]The spinous process serves to attachmusclesandligaments.

The two transverse processes, one on each side of the vertebral body, project laterally from either side at the point where the lamina joins thepedicle,between the superior and inferior articular processes.[7]They also serve for the attachment of muscles and ligaments, in particular theintertransverse ligaments.There is a facet on each of the transverse processes of thoracic vertebrae which articulates with thetubercle of the rib.[8]A facet on each side of the thoracic vertebral body articulates with thehead of the rib.The transverse process of alumbar vertebrais also sometimes called thecostal[9][10]orcostiform process[11]because it corresponds to a rudimentary rib (costa) which, as opposed to the thorax, is not developed in the lumbar region.[11][12]

There are superior and inferiorarticularfacet jointson 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 thepars interarticularis.

Regional variation

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Segments of the vertebrae

Vertebrae take their names from the regions of the vertebral column that they occupy. There are usually thirty-three vertebrae in the human vertebral column — sevencervical vertebrae,twelvethoracic vertebrae,fivelumbar vertebrae,five fusedsacral vertebraeforming thesacrumand fourcoccygeal vertebrae,forming thecoccyx.Excluding rare deviations, the total number of vertebrae ranges from 32 to 35.[13]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.[14][15]The most frequent deviations are eleven (rarely thirteen) thoracic vertebrae, four or six lumbar vertebrae and three or five coccygeal vertebrae (rarely up to seven).[15]

The regional vertebrae increase in size as they progress downward but become smaller in the coccyx.

Cervical

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Main article:Cervical vertebrae
A typical cervical vertebra

There are sevencervical vertebrae(but eight cervicalspinal 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 theatlas,and C2 is also called theaxis.The structure of these vertebrae is the reason why theneckandheadhave a large range of motion. Theatlanto-occipital jointallows theskullto move up and down, while theatlanto-axial jointallows 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 theforamen magnumto end in thecircle of Willis.These are the smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and oftenbifurcated(the spinous process of C7 is not bifurcated, and is substantially longer than that of the other cervical spinous processes).[16]

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, ananterior tubercleand aposterior tubercle,for the attachment of muscles. The front surface of the anterior arch is convex and its anterior tubercle gives attachment to thelongus colli muscle.The posterior tubercle is arudimentaryspinous process and gives attachment to therectus capitis posterior minor muscle.The spinous process is small so as not to interfere with the movement between the atlas and theskull.On the under surface is a facet for articulation with thedensof the axis.

Specific to the cervical vertebra is thetransverse foramen(also known asforamen transversarium). This is an opening on each of the transverse processes which gives passage to thevertebral arteryandveinand asympathetic 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 thecarotid tuberclebecause it separates thecarotid arteryfrom thevertebral artery.

There is a hook-shapeduncinate processon 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 backward off the vertebra below it and limits lateral flexion (side-bending).Luschka's jointsinvolve the vertebral uncinate processes.

The spinous process on C7 is distinctively long and gives the namevertebra prominensto this vertebra. Also acervical ribcan develop from C7 as ananatomical variation.

The termcervicothoracicis often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas.

Thoracic

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Main article:Thoracic vertebrae
A typical thoracic vertebra

The twelvethoracic vertebraeand their transverse processes have surfaces thatarticulatewith theribs.Some rotation can occur between the thoracic vertebrae, but their connection with therib cageprevents muchflexionor 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.

Thethoracolumbar spineor 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 thesuperior,transverseandinferior costal facets.As the vertebrae progress down the spine they increase in size to match up with the adjoining lumbar section.

Lumbar

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Main article:Lumbar vertebrae
Lumbar vertebra showing mammillary processes
A typical lumbar vertebra

The fivelumbar vertebraeare the largest of the vertebrae, their robust construction being necessary for supporting greater weight than the other vertebrae. They allow significantflexion,extensionand moderate lateral flexion (side-bending). The discs between these vertebrae create a naturallumbarlordosis(a spinal curvature that is concave posteriorly).[citation needed]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 lateralcostiform process,amammillary processand anaccessory process.[17]The superior, or upper tubercle is the mammillary process which connects with the superior articular process. Themultifidus muscleattaches 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 termlumbosacralis often used to refer to the lumbar and sacral vertebrae together, and sometimes includes their surrounding areas.

Sacral

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Sacrum
Main article:Sacrum

There are fivesacral vertebrae(S1–S5) which are fused in maturity, into one large bone, thesacrum,with nointervertebral discs.[18]The sacrum with theiliumforms asacroiliac jointon each side of thepelvis,which articulates with thehips.

Coccygeal

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Main article:Coccyx

The last three to fivecoccygeal vertebrae(but usually four) (Co1–Co5) make up the tailbone orcoccyx.[19]There are nointervertebral discs.

Development

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Development of vertebrae

Somitesform in the earlyembryoand some of these develop into sclerotomes. The sclerotomes form the vertebrae as well as the rib cartilage and part of theoccipital bone.From their initial location within the somite, the sclerotome cells migrate medially toward thenotochord.These cells meet the sclerotome cells from the other side of theparaxial mesoderm.The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body.[20]From this vertebral body, sclerotome cells move dorsally and surround the developingspinal cord,forming thevertebral arch.Other cells move distally to the costal processes ofthoracic vertebraeto form the ribs.[20]

Function

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Functions of vertebrae include:

  1. Support of the vertebrae function in the skeletomuscular system by forming the vertebral column to support the body
  2. Protection. Vertebrae contain avertebral foramenfor the passage of the spinal canal and its enclosedspinal cordand coveringmeninges.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.
  3. Movement. The vertebrae also provide the openings, the intervertebral foramina which allow the entry and exit of thespinal 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 theligamenta flava.Working together in the vertebral column their sections provide controlled movement and flexibility.
  4. Feeding of the intervertebral discs through the reflex (hyaline ligament) plate that separates the cancellous bone of the vertebral body from each disk

Clinical significance

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There are a number ofcongenital 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, calledhemivertebraecan cause an angle to form in the spine which can result in the spinal curvature diseases ofkyphosis,scoliosisandlordosis.Severe cases can cause spinal cord compression.Block vertebraewhere some vertebrae have become fused can cause problems.Spina bifidacan result from the incomplete formation of the vertebral arch.

Spondylolysisis a defect in thepars interarticularisof 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 aslipped disc,is the result of a tear in the outer ring (anulus fibrosus) of theintervertebral disc,which lets some of the soft gel-like material, thenucleus pulposus,bulge out in ahernia.This may be treated by aminimally-invasive endoscopic procedurecalledTessys method.

Alaminectomyis a surgical operation to remove the laminae in order to access the spinal canal.[21]The removal of just part of a lamina is called alaminotomy.

Apinched nervecaused by pressure from a disc, vertebra or scar tissue might be remedied by aforaminotomyto broaden the intervertebral foramina and relieve pressure. It can also be caused by a foraminastenosis,a narrowing of the nerve opening, as a result ofarthritis.

Another condition isspondylolisthesiswhen one vertebra slips forward onto another. The reverse of this condition isretrolisthesiswhere one vertebra slips backward onto another.

The vertebral pedicle is often used as a radiographic marker and entry point invertebroplasty,kyphoplasty,andspinal fusionprocedures.

Thearcuate foramenis a commonanatomical variationmore frequently seen in females. It is a bonybridgefound on the first cervical vertebra, the atlas where it covers the groove for thevertebral artery.[22]

Degenerative disc diseaseis 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

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Regions of vertebrae in thegoat

In other animals, the vertebrae take the same regional names except for the coccygeal – in animals with tails, the separate vertebrae are usually called thecaudal vertebrae.[19]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 upward 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 theelephant,the vertebrae are connected by tight joints, which limit the backbone's flexibility. Spinous processes are exaggerated in some animals, such as theextinctDimetrodonandSpinosaurus,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.[23]

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.[24]These vertebrae are most often found inreptiles,[25][26]but are found in someamphibianssuch as frogs.[27]The vertebrae fit together in a ball-and-socket articulation, in which the convex articular feature of ananteriorvertebra acts as the ball to the socket of a caudal vertebra.[25]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 themusclesurrounding thevertebral columndoes not lead to an opening between vertebrae.[27]

In many species, though not in mammals, thecervical vertebraebear ribs. In many groups, such aslizardsandsaurischiandinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. Thetransverse processesof mammals are homologous to the cervical ribs of otheramniotes.In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming.[28][29]Allmammalsexceptmanateesandslothshave seven cervical vertebrae, whatever the length of the neck.[30]This includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example.Birdsusually have more cervical vertebrae with most having a highly flexible neck consisting of 13–25 vertebrae.

In all mammals, thethoracic vertebraeare connected toribsand 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 thehead of a rib.There is also a facet on each of the transverse processes which articulates with thetubercle of a rib.The number of thoracic vertebrae varies considerably across the species.[31]Mostmarsupialshave thirteen, butkoalasonly have eleven.[32]The usual number is twelve to fifteen inmammals,(twelve in thehuman), though there are from eighteen to twenty in thehorse,tapir,rhinocerosandelephant.In certain sloths, there is an extreme number of twenty-five and at the other end only nine in thecetacean.[33]

There are fewerlumbar vertebraeinchimpanzeesandgorillas,which have three in contrast to the five in the genusHomo.This reduction in number gives an inability of the lumbar spine tolordosebut gives an anatomy that favours vertical climbing, and hanging ability more suited to feeding locations in high-canopied regions.[34]Thebonobodiffers by having four lumbar vertebrae.

Caudalvertebraeare the bones that make up the tails of vertebrates.[35]They range in number from a few to fifty, depending on the length of the animal's tail. In humans and other taillessprimates,they are called thecoccygeal vertebrae,number from three to five and are fused into thecoccyx.[36]

Additional images

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  • 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
  • Vertebrae anatomy

See also

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References

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This article incorporates text in thepublic domainfrompage 96of the 20th edition ofGray's Anatomy(1918)

  1. ^McGraw-Hill Science and Technology[full citation needed]
  2. ^O'Rahilly, Müller, Carpenter & Swenson."Chapter 39: The vertebral column".Basic Human Anatomy.www.dartmouth.edu.{{cite web}}:CS1 maint: multiple names: authors list (link)
  3. ^Dorland's (2012).Dorland's Illustrated Medical Dictionary(32nd ed.). Elsevier Saunders. p. 329.ISBN978-1-4160-6257-8.
  4. ^Gdyczynski, C.M.; Manbachi, A.; et al. (2014). "On estimating the directionality distribution in pedicle trabecular bone from micro-CT images".Physiological Measurement.35(12): 2415–2428.Bibcode:2014PhyM...35.2415G.doi:10.1088/0967-3334/35/12/2415.PMID25391037.S2CID206078730.
  5. ^Muller-Gerbl, M; et al. (Mar 2008)."The distribution of mineral density in the cervical vertebral endplates".Eur Spine J.17(3): 432–438.doi:10.1007/s00586-008-0601-5.PMC2270387.PMID18193299.
  6. ^Taylor, Tim."Lumbar Vertebrae".InnerBody.RetrievedMay 7,2017.
  7. ^abcCramer, Gregory D. (2014). "General Characteristics of the Spine".Clinical Anatomy of the Spine, Spinal Cord, and Ans.pp. 15–64.doi:10.1016/b978-0-323-07954-9.00002-5.ISBN978-0-323-07954-9.
  8. ^Standring, Susan (2008). "Thoracic vertebrae".Gray's Anatomy.p. 746.
  9. ^Platzer (2004), pp 42–43
  10. ^Latincostarefers to either a "rib" or "side" of the body. (Diab (1999), p 76)
  11. ^abTweedie, A.The library of medicinep. 31
  12. ^Heinz Feneis, Wolfgang Dauber (2000)Pocket Atlas of Human Anatomy: Based on the International Nomenclaturep. 2
  13. ^Watson, Charles; Kayalioglu, Gulgun (2009). "The Organization of the Spinal Cord".The Spinal Cord.pp. 1–7.doi:10.1016/B978-0-12-374247-6.50005-5.ISBN978-0-12-374247-6.
  14. ^Hu, Zongshan; Zhang, Zhen; Zhao, Zhihui; Zhu, Zezhang; Liu, Zhen; Qiu, Yong (August 2016)."A neglected point in surgical treatment of adolescent idiopathic scoliosis: Variations in the number of vertebrae".Medicine.95(34): e4682.doi:10.1097/MD.0000000000004682.PMC5400342.PMID27559975.
  15. ^abYing-zhao, Yan; et al. (February 2022)."Variation in Global Spinal Sagittal Parameters in Asymptomatic Adults with 11 Thoracic Vertebrae, four Lumbar Vertebrae, and six Lumbar Vertebrae".Orthopaedic Surgery.14(2). John Wiley & Sons: 341–348.doi:10.1111/os.13185.PMC8867438.PMID34935276.
  16. ^Cramer, Gregory D. (2014). "The Cervical Region".Clinical Anatomy of the Spine, Spinal Cord, and Ans.pp. 135–209.doi:10.1016/b978-0-323-07954-9.00005-0.ISBN978-0-323-07954-9.
  17. ^Postacchini, Franco (1999)Lumbar Disc Herniationp. 19
  18. ^Drake et al,Gray's Anatomy for Students,Churchill Livingstone/Elsevier (2010), 2nd edition, chapter 2
  19. ^abWeisberger, Mindy (March 23, 2024)."Why don't humans have tails? Scientists find answers in an unlikely place".CNN.Archivedfrom the original on March 24, 2024.RetrievedMarch 24,2024.
  20. ^ab Walker, Warren F., Jr. (1987)Functional Anatomy of the VertebrateSan Francisco: Saunders College Publishing.
  21. ^Dorland's (2012).Dorland's Illustrated Medical Dictionary(32nd ed.). Elsevier Saunders. p. 1003.ISBN978-1-4160-6257-8.
  22. ^Cakmak, O; et al. (Sep 2005). "Arcuate foramen its clinical significance".Saudi Med J.26(9): 1409–13.PMID16155658.
  23. ^Kardong, Kenneth V. (2002).Vertebrates: comparative anatomy, function, evolution.McGraw-Hill. pp.288–289.ISBN978-0-07-290956-2.
  24. ^Romer, Alfred (1962).The Vertebrate Body(3 ed.). Philadelphia, Pa; London, W.C.I.: W.B. Saunders Company.
  25. ^abParker, W. K. (1881)."Abstract Of Lectures On The Structure Of The Skeleton In The Sauropsida".The British Medical Journal.1(1053): 329–330.doi:10.1136/bmj.1.1053.329.JSTOR25256369.PMC2263429.
  26. ^Romer, Alfred (1956).Osteology of the Reptiles.Malabar, Florida: Krieger Publishing Company. pp. 0–89464–985–X.
  27. ^abKardong, Kenneth V. (2015).Vertebrates: Comparative Anatomy, Function, Evolution(7 ed.). New York, NY: McGraw-Hill Education.ISBN978-0-07-802302-6.
  28. ^"Beluga Whale".Yellowmagpie.com. 2012-06-27.Retrieved2012-08-12.
  29. ^"About Whales".Whalesalive.org.au. 2009-06-26.Retrieved2013-08-12.
  30. ^Dierauf, Leslie; Gulland, Frances M. D. (June 27, 2001).CRC Handbook of Marine Mammal Medicine: Health, Disease, and Rehabilitation, Second Edition.CRC Press.ISBN9781420041637.RetrievedMay 7,2017.
  31. ^Hyman, Libbie (1922).Comparative Vertebrate Anatomy.Chicago: University of Chicago Press. pp.123.
  32. ^"Physical Characteristics of the Koala".Australian Koala Foundation.Retrieved1 February2012.
  33. ^Hyman (1922), p. 124
  34. ^Lovejoy, C.O and McCullum, M.A. (2010)."Spinopelvic pathways to bipedality:why no hominids ever relied on a bent-hip-bent-knee gait".Philosophical Transactions of the Royal Society of London B: Biological Sciences.365(1556): 3289–99.doi:10.1098/rstb.2010.0112.PMC2981964.PMID20855303.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  35. ^Kardong, Kenneth V. (2002).Vertebrates: comparative anatomy, function, evolution.McGraw-Hill. pp.287–288.ISBN978-0-07-290956-2.
  36. ^Hyman, Libbie (1922).Comparative Vertebrate Anatomy.Chicago: University of Chicago Press. pp.125.
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