Musculoskeletal System - Axial Skeleton Development

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Adult axial skeleton

During the third week the paraxial mesoderm forms into "balls" of mesoderm paired either side of the neural groove, called somites, that are patterned by the notochord. Similar regions of each somite differentiate initially into 2 parts: the dermomyotome (dermal and muscle component) and the sclerotome (forms vertebral column). Each somite undergoes a segmental shift to form a vertebral body and the intervertebral disc.

The sclerotome mesenchyme first differentiates to form cartilage, that ossifies through endochondral ossification to form bone. The vertebral body begins as a bony collar that expands into regions of dying cartilage. The vertebral arch, enclosing the spinal cord, forms later and the arch remains open dorsally (linked by a ligament) to allow continued growth of the spinal cord.

The axial skeleton consists of: Skull, Auditory Ossicles, Hyoid bone, Vertebral column, Chest (sternum, ribs)

The vertebral column is a series of bone segments (vertebra) separated by specialized joints (intervertebral disc).

In the adult, the vertebra form rostro-caudally: 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, coccyx. There has been identified a population variability in the distribution of the number of vertebra.

Skeletal ossification continues postnatally, through puberty until mid-20s. Abnormalities of vertebral column development can lead to defects including scoliosis.

Musculoskeletal Links: Introduction | Mesoderm | Somitogenesis | Limb | Cartilage | Bone | Bone Timeline | Axial Skeleton | Skull | Joint | Muscle | Muscle Timeline | Tendon | Diaphragm | Lecture - Musculoskeletal Development | Lecture Movie | Abnormalities | Limb Abnormalities | Cartilage Histology | Bone Histology | Skeletal Muscle Histology | Category:Musculoskeletal
Historic Musculoskeletal Embryology  
1902 - Pubo-femoral Region | Spinal Column and Back | Body Segmentation | Cranium | Body Wall, Ribs, and Sternum | Limbs | 1901 - Limbs | 1902 - Arm Development | 1906 Human Embryo Ossification | 1906 Lower limb Nerves and Muscle | 1907 - Muscular System | Skeleton and Limbs | 1908 Vertebra | 1909 Mandible | 1910 - Skeleton and Connective Tissues | Muscular System | Coelom and Diaphragm | 1913 Clavicle | 1920 Clavicle | 1921 - External body form | Connective tissues and skeletal | Muscular | Diaphragm | 1929 Rat Somite | 1932 Pelvis | 1940 Synovial Joints | 1943 Human Embryonic, Fetal and Circumnatal Skeleton | 1947 Joints | 1949 Cartilage and Bone | 1957 Chondrification Hands and Feet | 1968 Knee

Historic Embryology: 1908 Vertebrae | 1910 Vertebral Column | 1914 Thoracic Vertebrae

Some Recent Findings

  • Ossification of the vertebral column in human foetuses: histological and computed tomography studies[1] "There is no agreement in the literature as to the time of the onset and progress of the vertebral column ossification. The aim of the present study was to determine the precise sequence of ossification of the neural arches and vertebral centra.Histological and radiographic studies were performed on 27 human foetuses aged from 9 to 21 weeks. It was found that the ossification of vertebrae commences in foetuses aged 10 and 11 weeks. Ossification centres appear first for neuralarches in the cervical and upper thoracic vertebrae and by the end of 11th week they are present in all thoracic and lumbar neural arches. In the vertebral centrain foetus of 10 weeks ossification was found in the lower 7 thoracic and first lumbar vertebrae. By the end of 11th week ossification is present in the lower 4 cervical, all thoracic, all lumbar and 4 sacral vertebral centra."
  • Foxa1 and foxa2 are required for formation of the intervertebral discs[2] "The intervertebral disc (IVD) is composed of 3 main structures, the collagenous annulus fibrosus (AF), which surrounds the gel-like nucleus pulposus (NP), and hyaline cartilage endplates, which are attached to the vertebral bodies. ... The NP forms from the embryonic notochord. Foxa1 and Foxa2, transcription factors in the forkhead box family, are expressed early during notochord development. ...Embryos lacking only Foxa1 or Foxa2 from the notochord were indistinguishable from control animals, demonstrating a functional redundancy for these genes in IVD formation. In addition, we provide in vivo genetic evidence that Foxa genes are required for activation of Shh in the notochord."
  • Role of environmental factors in axial skeletal dysmorphogenesis[3] "Approximately 1 in 1000 live births is afflicted with an axial skeletal defect. Although many of the known human teratogens can produce axial skeletal defects, the etiology of over half of the observed defects is unknown."
  • Embryology and bony malformations of the craniovertebral junction.[4] "The embryology of the bony craniovertebral junction (CVJ) is reviewed with the purpose of explaining the genesis and unusual configurations of the numerous congenital malformations in this region. ...A logical classification of this seemingly unwieldy group of malformations is thus possible based on their ontogenetic lineage, morbid anatomy, and clinical relevance. Representative examples of the main constituents of this classification scheme are given, and their surgical treatments are selectively discussed."
More recent papers  
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  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
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References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

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Search term: Axial Skeleton Development

Kelvin Manuel Piña Batista, Kenia Yoelvi Alvarez Reyes, Fátima Pérez Lopez, Andrés Coca Pelaz, Ivan Fernandez Vega, José Luis Llorente Pendás, Antonio Saiz Ayala, Aurora Astudillo, Jorge Andrés Nuñez Rojas, Patricia Barrio Fernandez Immunophenotypic features of dedifferentiated skull base chordoma: An insight into the intratumoural heterogeneity. Contemp Oncol (Pozn): 2017, 21(4);267-273 PubMed 29416431

Doris K Powe, Asok K Dasmahapatra, Joseph L Russell, Paul B Tchounwou Toxicity implications for early life stage Japanese medaka (Oryzias latipes) exposed to oxyfluorfen. Environ. Toxicol.: 2018; PubMed 29385312

Alex J Drew, Morgan T Izykowski, Kent N Bachus, Heath B Henninger, K Bo Foreman Transhumeral loading during advanced upper extremity activities of daily living. PLoS ONE: 2017, 12(12);e0189418 PubMed 29261703

Jeremie Silvent, Anat Akiva, Vlad Brumfeld, Natalie Reznikov, Katya Rechav, Karina Yaniv, Lia Addadi, Steve Weiner Zebrafish skeleton development: High resolution micro-CT and FIB-SEM block surface serial imaging for phenotype identification. PLoS ONE: 2017, 12(12);e0177731 PubMed 29220379

Bin Yang, Junlong Zhang, Lixin Li, Xiaojun Lyu, Wei Wei, Zhuochun Huang, Bei Cai, Lanlan Wang Genetic variations in LIGHT are associated with susceptibility to ankylosing spondylitis in a Chinese Han population. Oncotarget: 2017, 8(53);91415-91424 PubMed 29207654


Developing vertebra
  • The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter 15 the skeletal system
  • Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 11 Limb Dev (bone not well covered in this textbook)
  • Before we Are Born (5th ed.) Moore and Persaud Chapter 16,17: p379-397, 399-405
  • Essentials of Human Embryology Larson Chapter 11 p207-228


  • Identify the components of a somite and the adult derivatives of each component.
  • Give examples of sites of (a) endochondral and (b) intramembranous ossification and to compare these two processes.
  • Identify the general times (a) of formation of primary and (b) of formation of secondary ossification centres, and (c) of fusion of such centres with each other.
  • Briefly summarise the development of the limbs.
  • Describe the developmental abnormalities responsible for the following malformations: selected growth plate disorders; congenital dislocation of the hip; scoliosis; arthrogryposis; and limb reduction deformities.

Development Overview

Below is a very brief overview using simple figures of 3 aspects of early musculoskeletal development. More detailed overviews are shown on other notes pages Mesoderm and Somite, Vertebral Column, Limb in combination with serial sections and Carnegie images.

Mesoderm Development

Mesoderm cartoon 01.jpg Cells migrate through the primitive streak to form mesodermal layer. Extraembryonic mesoderm lies adjacent to the trilaminar embryo totally enclosing the amnion, yolk sac and forming the connecting stalk.
Mesoderm cartoon 02.jpg Paraxial mesoderm accumulates under the neural plate with thinner mesoderm laterally. This forms 2 thickened streaks running the length of the embryonic disc along the rostrocaudal axis. In humans, during the 3rd week, this mesoderm begins to segment. The neural plate folds to form a neural groove and folds.
Mesoderm cartoon 03.jpg Segmentation of the paraxial mesoderm into somites continues caudally at 1 somite/90minutes and a cavity (intraembryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.

Note intraembryonic coelomic cavity communicates with extraembryonic coelom through portals (holes) initially on lateral margin of embryonic disc.

Mesoderm cartoon 04.jpg Somites continue to form. The neural groove fuses dorsally to form a tube at the level of the 4th somite and "zips up cranially and caudally and the neural crest migrates into the mesoderm.

Somite Development

Mesoderm cartoon 05.jpg Mesoderm beside the notochord (axial mesoderm, blue) thickens, forming the paraxial mesoderm as a pair of strips along the rostro-caudal axis.
Mesoderm cartoon 06.jpg Paraxial mesoderm towards the rostral end, begins to segment forming the first somite. Somites are then sequentially added caudally. The somitocoel, is a cavity forming in early somites, which is lost as the somite matures.
Mesoderm cartoon 07.jpg Cells in the somite differentiate medially to form the sclerotome (forms vertebral column) and dorsolaterally to form the dermomyotome.
Mesoderm cartoon 08.jpg The dermomyotome then forms the dermotome (forms dermis) and myotome (forms muscle).

Neural crest cells migrate beside and through somite.

Mesoderm cartoon 09.jpg The myotome differentiates to form 2 components dorsally the epimere and ventrally the hypomere, which in turn form epaxial and hypaxial muscles respectively. The bulk of the trunk and limb muscle coming from the Hypaxial mesoderm. Different structures will be contributed depending upon the somite level.

Axial Features

  • human occipitocervical segmentation[5]
  • head and vertebral column boundary - located between the 5th and 6th somites[6]
  • craniovertebral junction - caudal occiput, atlas, and axis[7]

Embryonic Development

Week 8

Stage22 vertebra and spinal cord 1.jpg

Human embryo (Stage 22) vertebra and spinal cord development. Note the structure of the vertebral arch, the dorsal ligament allowing expansion of the arch to accommodate spinal cord growth.


Skull anterior.gif

See Skull Development

Links: Skull Development

Vertebral Column

Cervical Vertebra

Vertebral element ossification between species.[8]
  • C1 - (atlas) from fourth occipital and first cervical sclerotomes. Posterior arch ossifies from 2 centres in the lateral masses fusing postnatally between 3 - 5th years.

A comparison of vertebral element ossification between different species also in relation to Hox gene expression.[8]

  • For each taxon, circles indicate centra, and squares indicate left and right neural arches.
  • Colours represent the order of ossification.
  • Hox expression boundaries in the mouse (placentals) and vertebral segment identity are shown at right.
  • Conserved timing of V7 centrum ossification across mammals, including sloths (bradypus)
  • Overlap in Hox5-6 expression in the V6–V9 region of the sloth neck.

bradypus - three-toed sloths are the only members of this genus

dasypus - armadillo genus in the Dasypodidae family


Evolution of the sacrum[9] "In order to study the formation of the sacrum during the primate evolution, a new way of numbering mammalian vertebrae is presented; this demonstrates that the thoracolumbosacral complex is fixed at 22 vertebrae in 80% and at 22 +/- 1 in 100% of the cases. The shift of a vertebra from one type to another occurs either at the thoracolumbar or at the lumbosacral junction and not at the cervicothoracic junction. Rarely does the shift take place at the sacrococcygeal junction. Data from 318 primates reveal that the seven original lumbar vertebrae of the Old World monkeys are reduced in the great apes by a caudad "thoracization" of one to two lumbar vertebrae and a cephalad sacralization of one to four lumbar vertebrae. In the apes, sacralization is not total and different stages that are intermediate between lumbar and sacral are described. In Homo sapiens there is a total sacralization of the last two original lumbar vertebrae. In addition, development of the sacral wings (alae) is minimal in apes and reaches its maximum in hominids. The tendency of the hominoid sacrum to incorporate the last lumbar vertebrae and to widen markedly provides for an enhanced articulation of the sacrum with the ilium and offers a firm base of support for the trunk during erect posture. This is necessary for the support of the weight of the trunk above the sacrum and for the stabilization of the body during bipedal posture and locomotion. Encephalization did not play any major role in the widening of the sacrum since the former by far preceded the latter."

Intervertebral Disc

Mouse intervertebral disc (IVD) expression of transcription factor Nfatc1[10]

The adult intervertebral disc (IVD) has to bear the same loads as the vertebra and also have flexibility to allow axial column movement. This is achieved by a complex structure (cartilaginous end-plate) that links the vertebra above and below the disc to a outer dense fibrous structure (annulus fibrosus) containing a gel-like core region (nucleus pulposus). Some research in this area focusses on the degeneration of the IVD with ageing.

  • cartilaginous end-plate - that anchor the discs to the adjacent vertebral body bones
  • annulus fibrosus - cells are derived from the sclerotome
  • nucleus pulposus - cells are derived from the notochord[11]

Annulus Fibrosus

  • cells are derived from the sclerotome

Nucleus Pulposus

  • cells are derived from the notochord[11]
  • notochordal marker brachyury
  • proteoglycan rich extracellular matrix

Rib Development

Ribcage and Sternum

Mouse E12.5 Sox9 Expression.jpg

Sox9 expression in the Mouse (E12.5) rib primordial.[12]

Sternum Development

Whitehead RH. and Waddell JA. The early development of the mammalian sternum (1911) Amer. J Anat. 12: 89-106.


Like many other embryonic structures there are two separate considerations:

  1. Pattern Formation - sclerotome differentiation and segmentation
  2. Overt Differentiation - mesoderm differentiation to cartilage differentiation and ossification to bone.


Links: Notch

Nuclear factor of activated T-cells, cytoplasmic 1

Mouse intervertebral disc (IVD) expression of transcription factor Nfatc1[10]
  • Transcription factor (Nfatc1) has been identified in developing mouse intervertebral disc (IVD).
  • The NFAT family of transcription factors regulates cytokine gene expression by binding to the promoter/enhancer regions of antigen-responsive genes, usually in cooperation with heterologous DNA-binding partners.
  • The activation of NFAT proteins is controlled by calcineurin, the calmodulin-dependent phosphatase.
Links: OMIM - NFATC1

Transforming growth factor beta

Two functions in IVD development:[10]

  1. prevent chondrocyte differentiation in the presumptive IVD
  2. promote differentiation of annulus fibrosus from sclerotome


Spina Bifida

USA spina bifida rates.

Folic Acid and Neural Tube Defects

Absent Cervical Spine Pedicle

Absent cervical spine pedicle.jpg

Absent cervical spine pedicle[13]

The vertebral pedicles (Latin, pediculus ="small foot") are paired processes that project dorsally and connect the body of the spinal vertebra to the arch. Absence is a rare abnormality characterized by the absence of a pedicle of the affected vertebral body, seen most frequently at the level C6 followed by the level C5 and C7.


Historic image scoliosis (Braune 1877)
Chêneau Brace[15]

International Classification of Diseases

Q67 Congenital musculoskeletal deformities of head, face, spine and chest - Q67.5 Congenital deformity of spine Congenital scoliosis: NOS postural Excl.: infantile idiopathic scoliosis (M41.0) scoliosis due to congenital bony malformation (Q76.3)

Scoliosis.jpg Scoliosis xray.jpg

  • frequency of congenital scoliosis is approximately 0.5, or 1 in 1,000 births.
  • assymetric growth impairment of vertebral bodies
  • lateral deviation of spine (Lateral flexion, Forward flexion, Rotation of vertebral column on long axis)
  • compensated by movement of vertebral column above and below affected region (producing a primary and two secondary curves)
  • progresses rapidly in adolescence and becomes fixed once bone growth is completed.
  • both genetic and environmental terartogens implicated.
    • a large number of chromosomal deletions relating to regions 2p13 – 15, 6q13 and 15q12 have been identified.

Links: Musculoskeletal System - Abnormalities


  1. A Skórzewska, M Grzymisławska, M Bruska, J Lupicka, W Woźniak Ossification of the vertebral column in human foetuses: histological and computed tomography studies. Folia Morphol. (Warsz): 2013, 72(3);230-8 PubMed 24068685
  2. Jennifer A Maier, YinTing Lo, Brian D Harfe Foxa1 and Foxa2 are required for formation of the intervertebral discs. PLoS ONE: 2013, 8(1);e55528 PubMed 23383217 | PLOS One.
  3. Peter G Alexander, Rocky S Tuan Role of environmental factors in axial skeletal dysmorphogenesis. Birth Defects Res. C Embryo Today: 2010, 90(2);118-32 PubMed 20544699
  4. Dachling Pang, Dominic N P Thompson Embryology and bony malformations of the craniovertebral junction. Childs Nerv Syst: 2011, 27(4);523-64 PubMed 21193993 | PMC3055990 | { Childs Nerv Syst.]
  5. Fabiola Müller, Ronan O'Rahilly Segmentation in staged human embryos: the occipitocervical region revisited. J. Anat.: 2003, 203(3);297-315 PubMed 14529047
  6. B Christ, J Wilting From somites to vertebral column. Ann. Anat.: 1992, 174(1);23-32 PubMed 1605355
  7. Charles Raybaud Anatomy and development of the craniovertebral junction. Neurol. Sci.: 2011, 32 Suppl 3;S267-70 PubMed 21822704
  8. 8.0 8.1 Lionel Hautier, Vera Weisbecker, Marcelo R Sánchez-Villagra, Anjali Goswami, Robert J Asher Skeletal development in sloths and the evolution of mammalian vertebral patterning. Proc. Natl. Acad. Sci. U.S.A.: 2010, 107(44);18903-8 PubMed 20956304 | Proc Natl Acad Sci U S A.
  9. M M Abitbol Evolution of the sacrum in hominoids. Am. J. Phys. Anthropol.: 1987, 74(1);65-81 PubMed 3688211
  10. 10.0 10.1 10.2 Philip Sohn, Megan Cox, Dongquan Chen, Rosa Serra Molecular profiling of the developing mouse axial skeleton: a role for Tgfbr2 in the development of the intervertebral disc. BMC Dev. Biol.: 2010, 10;29 PubMed 20214815 | PMC2848151 | BMC Dev Biol.
  11. 11.0 11.1 Makarand V Risbud, Thomas P Schaer, Irving M Shapiro Toward an understanding of the role of notochordal cells in the adult intervertebral disc: from discord to accord. Dev. Dyn.: 2010, 239(8);2141-8 PubMed 20568241
  12. Nicholas W Plummer, Karsten Spicher, Jason Malphurs, Haruhiko Akiyama, Joel Abramowitz, Bernd Nürnberg, Lutz Birnbaumer Development of the mammalian axial skeleton requires signaling through the Gα(i) subfamily of heterotrimeric G proteins. Proc. Natl. Acad. Sci. U.S.A.: 2012, 109(52);21366-71 PubMed 23236180 | PMC3535641 | PNAS
  13. Roman Guggenberger, Gustav Andreisek, Hans Scheffel, Simon Wildermuth, Sebastian Leschka, Paul Stolzmann Absent cervical spine pedicle and associated congenital spinal abnormalities - a diagnostic trap in a setting of acute trauma: case report. BMC Med Imaging: 2010, 10;25 PubMed 21062465 | BMC Med Imaging.
  14. Sietke G Postema, Corry K van der Sluis, Kristina Waldenlöv, Liselotte M Norling Hermansson Body structures and physical complaints in upper limb reduction deficiency: a 24-year follow-up study. PLoS ONE: 2012, 7(11);e49727 PubMed 23226218 | PLoS One.
  15. Katarzyna Zaborowska-Sapeta, Ireneusz M Kowalski, Tomasz Kotwicki, Halina Protasiewicz-Fałdowska, Wojciech Kiebzak Effectiveness of Chêneau brace treatment for idiopathic scoliosis: prospective study in 79 patients followed to skeletal maturity. Scoliosis: 2011, 6(1);2 PubMed 21266084 | PMC3037926 | Scoliosis


Dachling Pang, Dominic N P Thompson Embryology and bony malformations of the craniovertebral junction. Childs Nerv Syst: 2011, 27(4);523-64 PubMed 21193993

Tadahiro Iimura, Nicolas Denans, Olivier Pourquié Establishment of Hox vertebral identities in the embryonic spine precursors. Curr. Top. Dev. Biol.: 2009, 88;201-34 PubMed 19651306

Tara Alexander, Christof Nolte, Robb Krumlauf Hox genes and segmentation of the hindbrain and axial skeleton. Annu. Rev. Cell Dev. Biol.: 2009, 25;431-56 PubMed 19575673

Moisés Mallo, Tânia Vinagre, Marta Carapuço The road to the vertebral formula. Int. J. Dev. Biol.: 2009, 53(8-10);1469-81 PubMed 19247958

Rochelle W Tyl, Neil Chernoff, John M Rogers Altered axial skeletal development. Birth Defects Res. B Dev. Reprod. Toxicol.: 2007, 80(6);451-72 PubMed 18157900


Timothy J Mead, Katherine E Yutzey Notch pathway regulation of chondrocyte differentiation and proliferation during appendicular and axial skeleton development. Proc. Natl. Acad. Sci. U.S.A.: 2009, 106(34);14420-5 PubMed 19590010

Susan Skuntz, Baljinder Mankoo, Minh-Thanh T Nguyen, Elisabeth Hustert, Atsuo Nakayama, Elisabeth Tournier-Lasserve, Christopher V E Wright, Vassilis Pachnis, Kapil Bharti, Heinz Arnheiter Lack of the mesodermal homeodomain protein MEOX1 disrupts sclerotome polarity and leads to a remodeling of the cranio-cervical joints of the axial skeleton. Dev. Biol.: 2009, 332(2);383-95 PubMed 19520072

Valerie Wilson, Isabel Olivera-Martinez, Kate G Storey Stem cells, signals and vertebrate body axis extension. Development: 2009, 136(10);1591-604 PubMed 19395637

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Search Pubmed: Axial Skeleton Development | Vertebra Development | Intervertebral Disc Development | Axial Skeleton Abnormalities

Additional Images


Human Embryology And Morphology (1921)
Keith, A. Human Embryology And Morphology (1921) Longmans, Green & Co.:New York.

5 Spinal Column and Back


  • centrum - (vertebral body) anatomical term referring to the main bony part of the vertebra that forms the majority of the axial skeleton.
  • haemal arch - referring to the bony arch region within animal tail vertebra that contains blood vessels.
  • idiopathic scoliosis - clinical term for a spinal column deformity appearing usually postnatally after the age of 10 years old.
  • lordosis - clinical and anatomy term describing the curvature of the spine with the convexity toward the front. Normal to have lordosis in the cervical and lumbar regions of the spinal column.
  • neural arch - referring to the bony arch region within vertebra that contains the spinal cord.
  • notochord sheath - region surrounding the notochord. in teleost fish direct mineralization of this region, by intramembranous ossification, forms the initial vertebral centrum. (More? Zebrafish Development)
  • rib hump - clinical term for the prominence formed by ribs on the convexity of a curve, caused by rotation of the spine and attached ribs.
  • spinal column - term referring to the musculoskeletal elements (vertebrae, ligaments, and intervertebral discs), that surround the spinal cord and form the axial skeleton.
  • synsacrum - in birds sacral and lumbar vertebrae fused region forming elongated sacral region.

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Cite this page: Hill, M.A. (2018, February 26) Embryology Musculoskeletal System - Axial Skeleton Development. Retrieved from

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