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.

See this series of articles by O'Rahilly, Müller and others on human vertebral column development using embryos from the Carnegie Collection.[1][2][3][4][5][6]

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

Axial Skeleton
skull (22) Auditory Ossicles (6) Hyoid bone (1) Vertebral Column (26) Thoracic cage (27)
  • cranial bones (8)
  • parietal (2)
  • temporal (2)
  • frontal (1)
  • occipital (1)
  • ethmoid (1)
  • sphenoid (1)
  • Cervical vertebrae (7)
  • Thoracic vertebrae (12)
  • Lumbar vertebrae (5)
  • Sacrum (1) - 5 at birth, later fused in adult stage
  • Coccyx (1) - 4 at birth, later fused to form one single bone, varies between 3-5
  • sternum (3) - manubrium (1) body of sternum (1) xiphoid process (1)
  • ribs (24)
Links: axial skeleton

Musculoskeletal Links: Introduction | mesoderm | somitogenesis | limb | cartilage | bone | bone timeline | bone marrow | shoulder | pelvis | axial skeleton | skull | joint | skeletal muscle | muscle timeline | tendon | diaphragm | Lecture - Musculoskeletal | Lecture Movie | musculoskeletal abnormalities | limb abnormalities | developmental hip dysplasia | cartilage histology | bone histology | Skeletal Muscle Histology | Category:Musculoskeletal
Historic Embryology - Musculoskeletal  
1853 Bone | 1885 Sphenoid | 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 | 1908 Cervical 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

Some Recent Findings

  • Rib Cage Morphogenesis in the Human Embryo: A Detailed Three-Dimensional Analysis[7] "Formation of the skeletal structure in the human embryo has important consequences in terms of support, protection, and function of organs and other systems. We aimed to describe the formation of the rib cage during the embryonic period, in order to detect prominent features and identify the possible factors affecting rib cage morphology. We employed high-resolution digitized imaging data (n = 34) obtained in human embryos with Carnegie stage (CS) between 17 and 23. The rib cage became detectable as cartilage formation at CS17, expanding outward from the dorsal side of the chest-abdominal region. Ribs elongated progressively to surround the chest, differentiating into the upper and lower rib cage regions by CS20. The ends of corresponding ribs in the upper region elongated toward each other, leading to their joining and sternum formation between CS21 and CS23, while the lower region of the rib cage remained widely open. The rib cage area with the largest width shifted from the 5th rib pair at CS17 to the 9th pair at CS23. The depth of the rib cage was similar across the upper region at CS17, with the major portion remaining in the middle part after CS20. The heart was located beneath the rib pairs providing the largest depth, while the liver was located beneath the rib pairs providing the largest width. Formation of the sternum, development of spinal kyphosis, and organization of larger internal organs within the thoracic and abdominal cavity are possible factors affecting rib cage morphology."
  • Evolutionary selection and morphological integration in the vertebral column of modern humans[8] "The main objective is to quantify integration, modularity, and response to selection in the presacral vertebral column of modern humans. Seventeen linear variables on each presacral vertebra were collected in 108 modern humans producing a total of ~39,000 measurements. Then, we studied patterns and magnitudes of integration at regional, vertebral, and intra-vertebral levels. Additionally, we calculated the ability of vertebrae to respond to selection by quantifying differences in evolvability, flexibility, and constraint throughout the spine. The results indicate that caudal vertebrae are more evolvable than those located more cranially in the presacral vertebral column, following an increasing pattern of evolvability from the cervical to the lumbar region. Additionally, the atlas and fifth lumbar vertebra show the lowest values of integration, while central thoracic vertebrae display the highest magnitudes of integration. These results could be related to three main factors: body plan organization expressed by the Hox genes, the strong developmental constraints that determine the number of mammalian vertebrae, and, finally, the functional requirements of an adaptation to bipedal locomotion in the human lineage."
  • Ossification of the vertebral column in human foetuses: histological and computed tomography studies[9] "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."
More recent papers  
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More? References | Discussion Page | Journal Searches | 2019 References | 2020 References

Search term: Axial Skeleton Development | Vertebral Column Development | Vertebra Development | Intervertebral Disc Development | Rib Development | Scoliosis

Older papers  
These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.

See also the Discussion Page for other references listed by year and References on this current page.

  • Foxa1 and foxa2 are required for formation of the intervertebral discs[10] "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[11] "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.[12] "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."


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 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 (intra-embryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.

Note intra-embryonic coelomic cavity communicates transiently with extra-embryonic 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.


The sclerotome forms from the ventromedial portion (region) of each somite with a mesenchymal cell organisation. The left and right sclerotome from each somite level contributes the vertebra and intervertebral disc of the entire axial skeleton.

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[13]
  • head and vertebral column boundary - located between the 5th and 6th somites[14]
  • craniovertebral junction - caudal occiput, atlas, and axis[15]

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.[16]
  • 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.[16]

  • 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[17] "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[18]

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[19]

Annulus Fibrosus

  • cells are derived from the sclerotome

Nucleus Pulposus

  • cells are derived from the notochord[19]
  • notochordal marker brachyury
  • proteoglycan rich extracellular matrix

Rib Development

Embryonic rib development(Week 7, Stage 18, Human Embryo 109, length 11 mm.
Adult Ribcage and Sternum

Humans form 12 paired ribs from the cartilaginous costal processes of the developing thoracic vertebrae. Early rib development occurs at 7 weeks (((GA}} week 9) from lateral plate mesoderm and continues postnatal with secondary ossification centres appearing at 15 years of age.

A recent paper has looked at rib cage development[7] between embryonic Week 7 to Week 9, 17 to 23. First identifying cartilage formation at CS1717 that expanding outward from the dorsal side of the chest-abdominal region. Ribs elongated progressively to surround the chest, differentiating into the upper and lower rib cage regions by CS20.

  • First 7 “true” ribs connect to the sternum through the costal cartilages about day 45.
  • Lower 5 “false” ribs do not connect to the sternum.


Sox9 expression in the Mouse (E12.5) rib primordial.[20]

Historic Rib papers  
Bardeen CR. XI. Development of the Skeleton and of the Connective Tissues in Keibel F. and Mall FP. Manual of Human Embryology I. (1910) J. B. Lippincott Company, Philadelphia.

Chondrogenous Period and Rib Development

"Ossification begins in the ribs before it does in the vertebrae. Centres appear in the bodies of the sixth and seventh ribs toward the end of the second month and then rapidly come to view in the other ribs. The centre in the first rib usually appears before that in the twelfth. All are usually present by the end of the second month, but that in the twelfth may not appear until later. In two specimens out of 29 fetuses with an estimated age of 55 to 110 days, Mall (1906) found a centre of ossification in the costal element of the seventh cervical vertebra."

Developmental rib abnormalities may be isolated or can occur with other congenital anomalies.

Sternum Development

The sternum and sternal ribs derive from the somatic layer of the lateral plate mesoderm.[21][22]

Historic Sternum papers  
Paterson The sternum - its early development and ossification in man and mammals. (1900) J Anat Physiol. 35(1): 21-32 PMID 17232454

Keith A. Human Embryology and Morphology. (1902) London: Edward Arnold. Body Wall, Ribs, and Sternum

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[18]
  • 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:[18]

  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[23]

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[25]

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: Scoliosis


 ICD-11 - LD2F.11 VATER association - VACTERL/VATER is an association of congenital malformations typically characterized by the presence of at least three of the following: vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities.

VACTERL/VATER are the acronyms used to describe a multi-system congenital malformations including at least three of the following:

  1. Vertebral defects
  2. Anal atresia
  3. Cardiac defects
  4. Tracheo-esophageal fistula
  5. Renal anomalies
  6. Limb abnormalities

VACTERL Clinical Diagnosis  
VACTERL/VATER Diagnostic Methods
Feature Intitial test(s) Notes
Vertebral anomalies X-ray; ultrasound and/or MRI of the spine X-ray may not show subtle spinal anomalies, and will be unable to detect associated anomalies such as tethered cord or syrinx
Anal atresia Physical examination/observation, abdominal ultrasound for genitourinary anomalies Additional testing is typically required to define anatomy, especially if concomitant genitourinary anomalies are present
Cardiac malformations Echocardiogram Other, more precise techniques, such as cardiac CT or MRI may be helpful to further detail anomalies
Tracheo-esophageal fistula Physical examination/observation (contrast studies are rarely required) Patients with VACTERL association but without true TEF may still present with swallowing/breathing anomalies, and clinicians should have a low index of suspicion for confirmatory radiological testing
Renal anomalies Renal ultrasound Further testing, such as a voiding cystouerethrogram, may be required in the presence of renal anomalies or if there is other evidence of issues such as vesicoureteral reflux
Limb anomalies Physical examination, X-ray Important not to overlook, as the presence of limb anomalies often prompts testing for Fanconi anemia
Suggested testing for patients (in addition to a careful physical examination by an experienced clinician) suspected to have VACTERL association. Specific modalities used should be dictated by the risk-benefit ratio for the specific situation.
Table reference [26]    Links: VACTERL | vertebra | heart | renal | limb

Sagittal Cleft Vertebra

Sagittal cleft vertebra, "butterfly vertebrae" or anterior rachischisis, is an abnormal vertebral body caused by failure of fusion of the 2 lateral chondrification centres during development. The term "butterfly vertebrae" is based upon the butterfly wings appearance of the 2 hemivertebrae on x-ray. See a recent review.{{#pmid"31448202|PMID31448202}}

Links: Sagittal Cleft Vertebra

Spondylocostal Dysostosis

A rare heritable axial skeleton growth disorder characterized by abnormal development of vertebra, multiple segmentation defects, and ribs.

Links: GeneReviews | Spondylocostal Dysostosis


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  7. 7.0 7.1 Okuno K, Ishizu K, Matsubayashi J, Fujii S, Sakamoto R, Ishikawa A, Yamada S, Yoneyama A & Takakuwa T. (2019). Rib Cage Morphogenesis in the Human Embryo: A Detailed Three-Dimensional Analysis. Anat Rec (Hoboken) , 302, 2211-2223. PMID: 31344324 DOI.
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  26. Solomon BD. (2011). VACTERL/VATER Association. Orphanet J Rare Dis , 6, 56. PMID: 21846383 DOI.


Pang D & Thompson DN. (2011). Embryology and bony malformations of the craniovertebral junction. Childs Nerv Syst , 27, 523-64. PMID: 21193993 DOI.

Iimura T, Denans N & Pourquié O. (2009). Establishment of Hox vertebral identities in the embryonic spine precursors. Curr. Top. Dev. Biol. , 88, 201-34. PMID: 19651306 DOI.

Alexander T, Nolte C & Krumlauf R. (2009). Hox genes and segmentation of the hindbrain and axial skeleton. Annu. Rev. Cell Dev. Biol. , 25, 431-56. PMID: 19575673 DOI.

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Mead TJ & Yutzey KE. (2009). Notch pathway regulation of chondrocyte differentiation and proliferation during appendicular and axial skeleton development. Proc. Natl. Acad. Sci. U.S.A. , 106, 14420-5. PMID: 19590010 DOI.

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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.
  • Cobb angle - clinical method of measuring the degree of scoliosis and post-traumatic kyphosis. Named after the American orthopedic surgeon John Robert Cobb (1903 - 1967) an American orthopedic surgeon.
  • 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)
  • 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.
  • thoracic hypokyphosis - term referring to the backward curve in the upper spine is to great, round back, Scheuermann's disease, or simply kyphosis.


Bone Terms  
Bone Development
  • canaliculi - (singular, canaliculus) small channel in the bone matrix in which an osteocyte process lies and communicates with other osteocytes and the Haversian canal. Allow osteocytes to communicate with each other and to exchange substances by diffusion.
  • cartilage - connective tissue from mesoderm in the embryo forms most of the initial skeleton which is replaced by bone. In adult, found on the surface of bone joints.
  • Cbfa1 - Core-Binding Factor 1 (Runx2) transcription factor protein key to the differentiation of bone OMIM: Cbfa1
  • centrum - the primordium of the vertebral body formed initially by the sclerotome.
  • circumferential lamellae - compact bone layers that underlie the periosteum and endosteum (endosteal lamellae). (see concentric and interstitial lamellae)
  • clavicle - (Latin, clavicle = little key) bone which locks shoulder to body.
  • Cobb angle - clinical term for measuring axial skeleton abnormality. Measures coronal plane deformity on antero-posterior plain radiographs in the classification of scoliosis. Named after the American orthopedic surgeon John Robert Cobb (1903 - 1967).
  • concentric lamellae - compact bone layers surrounding each osteon. (see interstitial and circumferential lamellae)
  • desmal ossification - (intramembranous ossification) the process of mesenchyme directly ossifying into bone without a pre-existing cartilage template. Vascularised regions of mesenchymal cells proliferate and differentiate into pre-osteoblasts and then osteoblasts, occurs in parts of the skull and the clavicle.
  • diaphysis - anatomical term that refers to the shaft of long bones.
  • endochondrial ossification - the process of replacement of the cartilagenous framework by osteoblasts with bone.
  • endosteum - inner layer of cells lining the medullary cavity of long bones and is highly vascularised. A similar cellular region and fibrous layer lies on the outside of the bone, the periosteum.
  • epiphysis - anatomical term that refers to the expanded ends of long bones.
  • extracellular matrix - material secreted by and surrounding cells. Consists if fibers and ground substance.
  • fibroblast growth factors - (FGF) a family of at least 10 secreted proteins that bind membrane tyrosine kinase receptors. A patterning switch with many different roles in different tissues. (FGF8 = androgen-induced growth factor (AIGF)
  • fibroblast growth factor receptor - receptors comprise a family of at least 4 related but individually distinct tyrosine kinase receptors (FGFR1- 4). They have a similar protein structure, with 3 immunoglobulin-like domains in the extracellular region, a single membrane spanning segment, and a cytoplasmic tyrosine kinase domain.
  • heterotopic ossification - (HO) a disorder of extra-skeletal bone formation that occurs as a complication of trauma or in rare genetic disorders. PMID28455214
  • haematopoiesis (Greek, haima = "blood"; poiesis = "to make") the process of blood cell formation. In the adult, this occurs only in the bone marrow. In the embryo this occurs in other locations (yolk sac, liver, spleen, thymus) until bone develops.
  • Haversian canal - the central canal of an osteon (Haversian system) in compact bone, within which blood vessels and nerves travel throughout the bone.
  • Haversian system - (osteon) the historic name for the functional unit of compact bone. Consists of a central canal (Haversian canal) surrounded by lamellar bone matrix within which osteocytes reside. Named after Clopton Havers (1650-1702) an English physician and anatomist. PMID12999959
  • Howship's lacuna - (resorptive bay) the historic name for the shallow bay or cavity lying directly under an osteoclast. This is the site of bone matrix resorption. Named after John Howship (1781–1841) a British anatomist who identified this region in 1820.
  • hyoid bone - part of the axial skeleton, is a U-shape bone in the neck that anchors the tongue and is associated with swallowing.
  • interstitial lamellae - compact bone layers that fill in between each osteon, interstitial lamellae, and do appear part of any Haversian system. (see concentric and circumferential lamellae)
  • intramembranous ossification - (desmal ossification) the process of mesenchyme directly ossifying into bone without a pre-existing cartilage template. Vascularised regions of mesenchymal cells proliferate and differentiate into pre-osteoblasts and then osteoblasts, occurs in parts of the skull and the clavicle.
  • lacuna - (Latin, lacuna = “ditch, gap” diminutive form of lacus = “lake”) lacunae is the plural, cavity in bone or cartilage for cell.
  • lamellar bone - the highly organized strong bone matrix deposited in concentric sheets with a low proportion of osteocytes. Many collagen fibers parallel to each other in the same layer. Replaces woven bone.
  • medullary cavity - (bone marrow) refers to the cavity within the bone, that is lined with cells (endosteum) and filled with bone marrow. in the adult, this can also be identified as either red or yellow marrow.
  • mesenchymal progenitor cells - (MPCs) cells able to differentiate in various types of connective tissue, including cartilage, bone and adipose tissue.
  • metaphysis - anatomical term that connecting region, that lies between the diaphysis and epiphysial line.
  • Moiré topography - clinical term for measuring axial skeleton abnormality. Measures spinal deviations using Moiré topography, a biosteriometric method producing a three-dimensional image of the shape of the trunk.
  • osteoblast - The mesenchymal cells that differentiate to form the cellular component of bone and produce bone matrix. Mature osteoblasts are called osteocytes. (More? bone)
  • osteoclast - Cells that remove bone (bone resorption) by enzymatically eroding the bone matrix. These cells are monocyte-macrophage in origin and fuse to form a multinucleated osteoclast. These cells allow continuous bone remodelling and are also involved in calcium and phosphate metabolism. The erosion cavity that the cells lie iwithin and form is called Howship's lacuna. (More? bone)
  • osteocyte - The mature bone-forming cell, which form the cellular component of bone and produce bone matrix. Differentiate from osteoblasts, mesenchymal cells that differentiate to form bone. (More? bone)
  • osteon - (Haversian system) the functional unit of compact bone. Consists of a central canal (Haversian canal) surrounded by lamellar bone matrix within which osteocytes reside.
  • pedicle - (Latin, pediculus = small foot) part of the vertebral arch forming the segment between the transverse process and the vertebral body.
  • periosteum - the cellular region and fibrous layer lying on the outside of the bone.
  • primary centre of ossification - the first area where bone growth occurs between the periosteum and cartilage.
  • resorptive bay - (Howship's lacuna) the shallow bay or cavity lying directly under an osteoclast. This is the site of bone matrix resorption.
  • sclerotome - ventromedial half of each somite that forms the vertebral body and intervertebral disc.
  • Scoliometry - clinical term for measuring axial skeleton abnormality using a Pedi-Scoliometer (Pedihealth Oy, Oulu, Finland) to measure spine deviation.
  • Sharpey’s fibres - (SF) “perforating fibres” provide anchorage for the periosteum and in tooth anchorage.
  • suture - in the skull a form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue.
  • trabecular bone - lamellar bone not forming Haversian systems.
  • woven bone - the first deposited weaker bone matrix with many osteocytes and a matrix disorganized structure. Replaced by lamellar bone. Seen in developing, healing and bone disease.
Other Terms Lists  
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