Carnegie stage 20

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Introduction

Stage20 bf1c.jpg

Facts

Week 8, 51 - 53 days, 18 - 22 mm

Gestational age GA week 10

Summary

  • Ectoderm: sensory placodes, lens pit, otocyst, nasal pits moved ventrally, fourth ventricle of brain
  • Mesoderm: heart prominence, ossification continues
  • Head: forebrain, eye, external acoustic meatus
  • hearing - otic capsule connected with the basal plate and with the future exoccipitals. Tip of the cochlea is elongated and curled. Tensor tympani and stapedius present.


See also Carnegie stage 20 Events

Features

  • scalp vascular plexus, eylid, eye, nose, external acoustic meatus, auricle of external ear, arm, elbow, wrist, liver prominence, digital rays
  • Identify: straightening of trunk, pigmented eye, eyelid, nose, external acoustic meatus, scalp vascular plexus, digital rays, liver prominance, thigh, ankle, foot plate, umbilical cord


Stage 20 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Category:Carnegie Stage 20 | Next Stage 21
  Historic Papers: 1914 head | 1954 Stage 19-23
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

Bright Field

Stage20 bf11.jpg Stage20 bf12.jpg

Stage20 bf13.jpg

Virtual Embryo Slides

Stage 20 - Right Lateral

Stage20 bf11.jpg

 ‎‎Mobile | Desktop | Original

Stage 20 | Embryo Slides
Stage 20 - Right Dorsolateral

Stage20 bf12.jpg

 ‎‎Mobile | Desktop | Original

Stage 20 | Embryo Slides
Stage 20 - Ventral

Stage20 bf13.jpg

 ‎‎Mobile | Desktop | Original

Stage 20 | Embryo Slides

Kyoto Collection

Stage20 bf1.jpg

View: This is a dorsolateral view of embryo. Amniotic membrane removed.

K10344

K15818


Movies

Stage20 MRI S05 icon.jpg
 ‎‎Sagittal Embryo
Page | Play
Stage20 MRI S02 icon.jpg
 ‎‎Sagittal Embryo
Page | Play


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

Stage20 bf2.jpg Stage20 bf3.jpg Stage20 bf4.jpg Stage20 bf5.jpg Stage20 bf6.jpg Stage20 bf7.jpg Stage20 bf8.jpg Stage20 bf9.jpg Stage20 bf10.jpg

Carnegie stage 20: 8517 Right | 8517 Anterior | 8517 Left | 7906 Right | 7906 Anterior | 7906 Left | 7274 Right | 7274 Anterior | 7274 Left


Carnegie Collection - Stage 20 
Serial No. Size (mm) Grade Fixative Embedding Medium Plane Thinness (µm) Stain Point Score Sex Year Notes
240 E, 20 Ch, 50x40x30 Poor Formol P Coronal 20 Iron H. 27 d 19??
256 E, 21 poor Alc p Sagittal 25 Coch. 23 M 1904 Tubal. Partial anencephaly
353 E, 20 Poor Alc P Sagittal 20 H. & Congo red 22,5 M 1906
431 E, 19 Ch, 30x25x25 Good Formol P Sagittal 20 H. & Congo red 25,5 M 1908 Tubal
437 E, 23 Ch., 80x60x50 Poor Formol P Sagittal 50 Coch 24 M 193?
453 E, 23 Ch, 60x40x30 Poor Formol P Sagittal 20 H. & Congo red 23-5  ? 1910 Injected
460 E, 21 Exc. Bichlor. acetic P Transverse 40 (Stain - Haematoxylin Eosin), coch, 24.5 M 1910 injected
462 E, 20 Ch, 50x40x30 Exc. Formol P Transverse 40 Al, coch 23.5 F 1910
635B E, 22 Poor Ale P Trans 50 Al, coch 26.5 M 1913
657 E, 25 Ch, 35x20x15 Poor Formol C Sagittal 40 Al, coch 26.5 M 1913 Tubal
966 E, 23 Ch, 51x38x13 Exc Bichlor. acetic P Coronal 40 (Stain - Haematoxylin Eosin), aur, or. G 25 M 1911 Tubal
1134B E, 23 Poor Formol p Sagittal 100 Al. coch., 22 - 1915
1266 E, 23.1 Poor Formol C-P Sagittal 25 Al. coch., (Stain - Haematoxylin Eosin) aur, or G 20.5 F 191?
2393 Ch, 61.5x50x35 Poor
3527 E., 22 Ch. 32x30x10 Good Formol P Sagittal 25 Al. coch., 28  ? 1921
4059 E, 21.6 Good Formol P Coronal 15 Al. coch., Mallory 29.5 $ 1922
4148 E, 21 Ch. 45x34x30 Good Formol p Coronal 15 A1. coch., Mallory 19  ? 1922
4361 E, 22 Ch., 52x42x23 poor Formol 9 Transverse 20 Coch. 24 8 1923
6202 E, 21 Ch., 35x35x22 Exc Bouin P Sagittal 20 (Stain - Haematoxylin Eosin) 20.5 8 1930 Tubal
6426 E 21.5 Good Formol C—P Transverse 20 (Stain - Haematoxylin Eosin) - 21 3 1931
7274 E, 18.5 Ch., 48x44x35 Exc Bouin C—P Transverse 20 (Stain - Haematoxylin Eosin), phlox. 20 M 1936
7906 E19.5 Exc Bouin C—P Coronal 20 (Stain - Haematoxylin Eosin) 22 8 1941 Left renal agenesis
8517 E., 20.8 Exc. Bouin C—P Coronal 20 (Stain - Haematoxylin Eosin) 24 8 1943
8226 E, 18.0 Exc. Bouin C—P Sagittal 10 Alan  ? 3 1944
Abbreviations
  • Size - E. is the greatest length of the embryo and Ch. is the mean diameter of the chorion.
  • 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)
  • Stain -
  •  ? - unknown or not determined.
iBook - Carnegie Embryos  
link=http://itunes.apple.com/au/book/the-carnegie-staged-embryos/id510004473?mt=11 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).

Blechschmidt Collection

Bl130758-01.jpg

Embryo (130758)


Links: Blechschmidt Collection

Madrid Collection

Madrid Collection Embryos  
Carnegie
Stage
Embryo Days CRL (mm) Section
thickness
Staining Section plane
20 CAS 20 49 20 10 (Stain - Haematoxylin Eosin)-Azan frontal
20 CN3 50 21 10 (Stain - Haematoxylin Eosin) transverse
20 BOT21 50 21 10 (Stain - Haematoxylin Eosin)-trichrome sagittal


Sydney University Collection

The following embryos were part of a 1943 study of testes development[2] Embryos based upon their CRL were probably Stage 20 to 21.

Embryo Crown Rump Length (mm) Gonad (mm) Groin distance (mm)
H 125 20 2.4 1.0
H 181 20.6 2.8 1.1
H 271 21 3.0 0.7
H 408 22 2.3 1.0

Events

  • Vision
    • (stage 19 -22) eyelid folds develop into the eyelids and cover more of the eye as the palpebral fissure takes shape. The upper and the lower eyelids meet at the outer canthus in Stage 19.[3]
    • Lens cavity is lost and a lens suture begins to form. The inner canthus is established.[3]
  • Cardiovascular
    • Cerebral artery the stem of the anterior cerebral artery gives rise to the olfactory artery.[4]
  • Endocrine System Development[5]
    • Hypophysis - the adenohypophysial epithelium adjacent to the neurohy- pophysis constitutes the beginning pars intermedia (O'Rahilly 1973 a). The walls of the craniopharyngeal pouch bud into the mesenchyme (An- dersen et al. 1971 ; Jir/tsek 1980).
    • Thymus - the right and left components are in contact with each other (Weller 1933)but are "never completely fused" (Norris 1938, Siegler 1969). Thymic cortex appears (in stages 20-22) as a result, according to Norris (1938), of migration of and covering by "cells derived from the cervical sinus".
    • Parathyroids - the parathyroid glands are attached to the lateral lobes of the thyroid (Weller 1933).

Weller (1933, Fig. 23) showed parathyroid 3 still rostral to parathyroid 4 at 23 mm, whereas (presumably due to variation in the "descent" of the thymus) Norris (1937, Fig. 4) showed parathyroid 3 rostral to, level with, and caudal to parathyroid 4 in embryos of 16-17 mm.

    • Thyroid - the "annectent bars" of the thyroid are more compact then previously (Weller 1933). The thyroid now exhibits its definitive external form.
  • Meninges (Spinal Cord) - increased chondrification ventral vertebral wall and greater concentration in the dorsal vertebral wall (the membrana reuniens), further ventral migration of the ganglia, and formation of large cavities in the meninx primitiva and a reticular arrangement of its cells. Layers of stratified cells overlying the dorsal surfaces of the centra and intervertebral disks, distinguishable in stage 17, 18, are now separated from these structures by a narrow network of loose cells. This stratified concentration of cells is the rudiment of the ventral dura mater, and may be traced both laterally and medially to the ganglia. The part lateral to the ganglia passes over into, and becomes indistinguishable from, the dense stratum of the meninx primitiva that forms the more dorsal canal wall. Passing caudad, the ventral dura mater rudiment lies in ever closer proximity to the centra and intervertebral disks, becoming continuous with these structures in the lower cervical segments. It can, however, be identified throughout the thoracic regions.[6]

References

  1. Streeter GL. Developmental Horizons In Human Embryos Description Or Age Groups XIX, XX, XXI, XXII, And XXIII, Being The Fifth Issue Of A Survey Of The Carnegie Collection. (1957) Carnegie Instn. Wash. Publ. 611, Contrib. Embryol., 36: 167-196.
  2. Wyndham NR. A morphological study of testicular descent. J Anat. 1943 Jan;77(Pt 2):179-188.3. No abstract available. PMID 17104926
  3. 3.0 3.1 Pearson AA. The development of the eyelids. Part I. External features. (1980) J. Anat.: 130(1): 33-42. PMID 7364662 PDF
  4. Khaled Menshawi, Jay P Mohr, Jose Gutierrez A Functional Perspective on the Embryology and Anatomy of the Cerebral Blood Supply. J Stroke: 2015, 17(2);144-58 PubMed 26060802 | J Stroke.
  5. O'Rahilly R. The timing and sequence of events in the development of the human endocrine system during the embryonic period proper. (1983) Anat. Embryol., 166: 439-451. PMID 6869855
  6. Sensenig EC. The early development of the meninges of the spinal cord in human embryos. (1951) Contrib. Embryol., Carnegie Inst. Wash. Publ. 611,

Additional Images

Historic Images

Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" 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 and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Lewis WH. The Cartilaginous Skull Of A Human Embryo Twenty-One Millimeters In Length. (1920) Contrib. Embryol., Carnegie Inst. Wash. Publ. 272, 9: 299-324.

Dickie JK. The anatomy of the head end of a 20 mm human embryo. (1914) J Anat Physiol., 48(4): 445-60. PMID 17233010

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. 2017 Embryology Carnegie stage 20. Retrieved October 24, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_20

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G