Carnegie stage 9

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A personal message from Dr Mark Hill (May 2020)  
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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!


Stage9 sem1.jpg


Human embryonic stage 9 occurs during week 3 between 19 to 21 days.

Gestational Age GA - week 5

The embryo is now 1.5 to 2.5 mm in size and somites have begun to form and number between 1 to 3 somite pairs during this stage.

The initial images are displayed unlabeled to allow you to explore the embryo for yourself, linked labeled versions are also available for some images.

See also Carnegie stage 9 image gallery.

Stage 9 Links: Week 3 | Gastrulation | Lecture | Somitogenesis | Lecture - Mesoderm | Lecture - Ectoderm | Lecture - Early Vascular | Science Practical | Carnegie Embryos | Category:Carnegie Stage 9 | Next Stage 10
  Historic Papers: 1920 | 1926 | 1945
Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline


  • Ectoderm - Neural plate brain region continues to expand, neural plate begins folding over the notochord. Gastrulation continues through the primitive streak region.
  • Mesoderm - Paraxial mesoderm segmentation into somites begins (1 - 3 somite pairs). Lateral plate mesoderm begins to vacuolate, dividing it into somatic and splanchnic mesoderm and to later form the intra-embryonic coelom. Prechordal splanchnic mesoderm begins to form the cardiogenic region, from which the primordial heart will develop.
  • Endoderm - Notochordal plate still visible which will form the notochord. Endoderm is still widely open to the yolk sac and germ cells form part of this layer. Extra-embryonic mesoderm on the yolk sac surface begins to form "blood islands".

See also Events


  • Neural groove and neural folds, the mesoderm, which segments beside the neural groove to form somites but extends laterally to margin of embryonic disc lateral plate mesoderm, where it merges with the covering extraembryonic mesoderm.
  • The intra-embryonic coelom develops in the middle of the lateral plate mesoderm. Note amniotic ectoderm covered by extra-emebryonic mesoderm (empty spaces above and below the mesoderm are artefacts, as are the lateral folds in the ectoderm).

The first two images using bright field microscopy approximate the orientation of the scanning electron micrographs below. There are additional scanning electron micrographs showing selected features in detail. Carnegie_stage_9 image gallery

Links: Week 3 | Gastrulation | Lecture | Practical | 1920 Carnegie No.1878 | Stage 10

Bright Field Lateral

Lateral View Ventrolateral View
Stage 9 View 1 Stage 9 View 2
Lateral View 1 - Large | 800px | Medium | Small Ventrolateral View 2 - Large | 800px | Medium | Small

Scanning EM Lateral

Lateral View Ventrolateral View
Stage 9 View 1 Stage 9 View 2
Lateral View 1 - Small | Medium | Large Ventrolateral View 2 - Small | Medium | Large

Notochordal plate

Stage9 sem3c.jpg

Notochordal plate - Small | Medium | Large

Bright Field Dorsal

Dorsal Ventral
Stage 9 View 3 Stage 9 View 4
Lateral View 1 - Small | Medium | Large Ventrolateral View 2 - Small | Medium | Large

Scanning EM Dorsal

Stage9 sem4c.jpg Stage9 sem5c.jpg Stage9 sem6c.jpg Stage9 sem7c.jpg

Kyoto Collection

Dorsal View Ventral View
Stage 9 View 1 Stage 9 View 2
Embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side. Embryonic disc, showing the epiblast, connecting stalk and brain fold.

Image source: UNSW Embryology page Created: 19.03.1999

Image source: The Kyoto Collection images are reproduced with the permission of Prof. Kohei Shiota and Prof. Shigehito Yamada, Anatomy and Developmental Biology, Kyoto University Graduate School of Medicine, Kyoto, Japan for educational purposes only and cannot be reproduced electronically or in writing without permission.

Carnegie Collection

Carnegie Collection - Stage 9 
Serial No. Pairs of somites Size (mm) Grade Fixative Embedding Medium Plane Thinness (µm) Stain Year Notes
1878 2-3 Embryo, 1.38
Ch., 12x10.5x7.5
Good Formol P Coronal 10 (Stain - Haematoxylin Eosin) 1917 Described by Ingalls (1920).[1]
5080 1 Embryo, 1.5
Ch., 14.5
Poor Formol P Transverse 10 Al. coch. 1926 Studied by Davis (1927).[2]
7650 2-3 Embryo, 2-3 Good Alc & Bouim C-P Transverse 6 (Stain - Haematoxylin Eosin) 1939 Said to be female[3]
  • Grade - total grade of the specimen and includes both its original quality and the condition of the mounted sections.
  • Embedding medium - paraffin (P) or a combination of celloidin and paraffin (C-P).
  • Fixative - formalin (Formol), alcohol and formalin (Alc, formol), Bouin (Bouin solution)
  •  ? - unknown or not determined.
  1. Ingalls, N.W. 1920. A human embryo at the beginning of segmentation, with special reference to the vascular system. Carnegie Instn. Wash. Publ. 274, Contrib. Embryol., 11, 61-90.
  2. Davis, C. L. 1927. Development of the human heart from its first appearance to the stage found in embryos of twenty paired somites. Carnegie Instn. Wash. Publ 380, Contrib. Embryol., 19, 245-284.
  3. PARK WW. (1957). The occurrence of sex chromatin in early human and macaque embryos. J. Anat. , 91, 369-73. PMID: 13448995
iBook - Carnegie Embryos  
link= iTunes link
  • iTunes link | iBook Store
  • Description - Imagine the excitement of seeing this incredible early period of human development for the first time. Now consider that much of our initial understanding of human development is based upon study of historic embryo collections. You can now look at these historic images of the first 8 weeks after fertilisation and explore for yourself the changes that occur in human development during this key period. This current book is designed as an atlas of the Carnegie embryo stages with some brief notes and additional information covering the first 8 weeks of development. These images are from from the beginning of last century and are one of the earliest documented series of human embryos collected for basic research and medical education on development. I hope you enjoy learning about the amazing early events that begin to make and shape us. This is the second book in a series of educational releases from UNSW Embryology.
  • Release: First Edition - Mar 12, 2012 ISBN 978-0-7334-3148-7 Print Length 82 Pages, 25.8 MB Language English.
  • PDF Preview version 3.87 MB (Read the associated information, this is an edited educational preview version with many features not functioning).
  • The current website also includes numerous embryo images from this textbook (see Embryonic Development and Carnegie Embryos).


  • hearing - otic placode (disc or otic zone) appears opposite the rhombencefhalic fold.[1][2]


Additional Images

Primordial germ cell region

Light Images

Scanning EM Images

SEM Dorsal

SEM Cranial Neural fold

SEM Caudal Region

SEM Caudal Region cross section

Image Source: Scanning electron micrographs of the Carnegie stages of the early human embryos are reproduced with the permission of Prof Kathy Sulik, from embryos collected by Dr. Vekemans and Tania Attié-Bitach. Images are for educational purposes only and cannot be reproduced electronically or in writing without permission.

Embryonic Development

Historic Stage 9 Embryos

Listed by number of pairs of somites.

1 somite Carnegie No. 5080. Studied and illustrated by Davis (1927, figs. 2–5 and 39–42) and Severn (1971, figs. 1–4). First pair of somites not separate rostrally and contain no myocoeles (Arey, 1938). Chorion, 14.5 x 1.5 mm. Embryonic disc, 1.5 mm. Reconstructed by Müller and O'Rahilly (1983, fig. 2).

1 somite A specimen described briefly by Baginski and Borsuk (1967).

1-2 somite (or more?), Carnegie No. 7650. Reconstructed by Müller and O'Rahilly (1983, fig. 5).

2 somites, Da 1 (Dann). An important specimen (fig. 9-2) possessing 2 pairs of somites (Studnicka, 1929; Florian and Völker, 1929; Arey, 1938)[1], although featured originally as having only one. Described and illustrated in detail by Ludwig (1928). Removed from uterus. Chorion, 12 mm. Embryo, 1.8 mm in a straight line, 2.4 mm by flexible scale. Sectioned transversely at 8 μm. Stained with alum cochineal. Neurenteric canal present. Sections are housed in the Anatomisches Institut, Basel. Photographs of sections are in Carnegie Collection under No. 5982. Presumed age, about 21 days. Dorsal and median projections published (ibid., figs. 1 and 2; Florian and Völker, 1929, fig. 14). Reconstructed by Müller and O’Rahilly (1983) fig. 3.

2–3 somites, H3. Described by Wilson (1914)[2], according to whom it “possessed probably two, possibly three, pairs of somites.” Chorion, 8.5 x 5.7 x 5 mm. Embryo, 1.43 mm. Sectioned obliquely (transversely) at 10 μm. Stained with hematoxylin. Fixation not adequate for reconstruction. The relatively longer primitive streak suggests that this embryo may be less advanced than No. 1878. Prechordal plate, or at least prechordal mesoderm, figured (Hill and Florian, 1931b)[3]. Presumed age, 18–21 days.

2/3 somites, Carnegie No. 1878 (figs. 9-3 to 9-7). An important specimen possessing 2 somites on the right side and 3 on the left. Florian (1934b) had certain difficulties and considered the embryo to be too small. Curettage. Chorion, 12 X 10.5 X 7.5 mm. Embryonic disc, 1.38 mm in a straight line. Described in detail and illustrated by Ingalls (1920) who believed that “the earliest recognizable stage of dextrocardia” is present, “to which might have been added later a more or less complete situs inversus viscerum”; at any rate, Davis (1927), who studied and illustrated the heart, considered that “the cardiac area is distorted.” Angiogenesis in chorion described by Hertig (1935). Primitive streak and node, 0.13 mm, according to Ingalls, but about 0.22 mm in fig. 15 of Florian and Völker (1929) and more than 0.3 mm in plate 5, fig. 9, of Bartelmez and Evans (1926)[4]. Neurenteric canal not patent but pit present (Bartelmez and Evans, 1926)[4]. Median projection published (ibid., plate 5, fig. 9; Florian and Völker, 1929, fig. 15; Müller and O’Rahilly, 1983, fig. 1).

3 somites, T439 (Toronto). Possesses 3 pairs of somites (Arey, 1938), although considered originally as having only 2. Described by Piersol (1939). Embryo (along surface), 2.03 x 0.72 mm. Sectioned sagitally. Neurenteric canal closed but its remains are identifiable. Primordial germ cells near allantois. Embryonic disc rostral to somites, including cardiac area, is retarded. Said to contain no blood vessels in any part of the embryo itself.

3 somites, Vant embryo. Described by Shaner (1945)[5], who found “two to three pairs of somites.” Embryo (along curve), 1.5 mm. Thought to be 25 ± 2 days. Reconstructed again from original sections by Müller and O’Rahilly (1983, fig. 4).

3 somites, Gv (Madrid). Described by Jiménez Collado and Ruano Gil (1963). Heart described by Orts Llorca, Jiménez Collado, and Ruano Gil (1960). Tubal. Embryo, 1.81 mm. Sectioned at 7 μm. Stained with hematoxylin and eosin. Reconstructed. On the basis of its external characters, said to lie between stage 9 and stage 10. Presumed age, 21 ± 1 days.

3 somites, No. 2008 (Prague). Excellent specimen (figs. 9-8 to 9-14) belonging to Dr. J. E. Jirásek. Embryo, 1.73 mm. Fixed in calcium formol. Sectioned transversely at 10 μm. Various stains used, including histochemical procedures. Should be published.

3 somites (?), His embryo E. This 2.1-mm specimen is listed by Bartelmez and Evans (1926)[4] between No. 1878 (2–3 somitic pairs) and No. 3709 (4 somitic pairs, stage 10).


Historic Images

Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

1920 Carnegie No.1878 A Human Embryo at the Beginning of Segmentation, with Special Reference to the Vascular System. By N. William Ingalls

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Cite this page: Hill, M.A. (2020, May 30) Embryology Carnegie stage 9. Retrieved from

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