1987 Developmental Stages In Human Embryos - Stage 21

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O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).

Online Editor Note  
O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).

The original 1987 publication text, figures and tables have been altered in formatting, addition of internal online links, and links to PubMed. Original Document - Copyright © 1987 Carnegie Institution of Washington.

See also the later 2010 paper by the same authors - O'Rahilly R & Müller F. (2010). Developmental stages in human embryos: revised and new measurements. Cells Tissues Organs (Print) , 192, 73-84. PMID: 20185898 DOI.

Links: Embryonic Development | Carnegie Collection | Carnegie Embryos | Ronan O'Rahilly | Fabiola Müller

1987 Stages: Introduction | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | References | Appendix 1 | Appendix 2 | Historic Papers | Embryonic Development
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
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)

Stage 21

Carnegie Collection - Stage 21 
Serial No. Size (mm) Grade Fixative Embedding Medium Plane Thinness (µm) Stain Point Score Sex Year Notes
22 E, 20 Ch, 35x30x30 Good Alc. P Transverse 50 Al. coch. 34.5 Female 1895
57 E, 23 Ch., ca. 30 Poor Alc. P Sagittal 50 Al. coch. 36 Male 1896
128 E, 20 Ch., 50x43 Good Formol P Coronal 50 Al. coch. 33 Female 1898
229 E, 19 Poor Alc. P Sagittal 50 Al. coch. 33 Female 1903
349 E, 24 Good Zenker C Coronal 250 Unstained 36 ? 1905 Double vascular injection
455 E, 24 Ch., 42x34x20 Good Alc. P Transverse 30 (Stain - Haematoxylin Eosin) 36.5 Male 1910
632 E, 24 Ch., 60x50x30 Good Bichlor. acetic P Sagittal 40, 100, 250 Al. coch. 33 Female 1913 Injected
903C E, 23.5 Good Formol P Transverse 40 Al. coch. 38.5 Female 1914
1008 E, 26,4 Good Formol P Sagittal 40 Al. coch. 39 ?? 1914
1358F E, 23 Good Formol P Sagittal 40 Al. coch. 37.5 Female 1916
2937 E,, 24.2 Good Bouin P Transverse 50 (Stain - Haematoxylin Eosin) aur., or. G. 39 Female 1920
3167 E., 24.5 Ch., 60x50x40 Poor Bichlor, acetic, formol P Transverse 20 Al. coch. 32 Male 1920
4090 E, 22.2 Ch.. 66x46x30 Good Formol P Transverse 40 Al. coch. 30 Female 1922
4160 E,25 Poor Formol P Sagittal 25 (Stain - Haematoxylin Eosin) 39 Male 1923 Tubal
4960 E.22 Ch,, 47x42x28 Good Formol P Transverse 15 Al. coch., Mallory 31.5 Female 1925
5??6 E. 215 Good Formol P Sagittal 20 (Stain - Haematoxylin Eosin) 34 Female 1927
6531 E,22 Poor Glacial acetic, C-P Transverse 10 (Stain - Haematoxylin Eosin) 31.5 Female 1931 Leitz Collection
7254 E,225 Exc Bouin C-P Transverse 20 (Stain - Haematoxylin Eosin) 33.5 Male 1936
7592 E,22-> Exc. Bouin C-P Transverse 20 (Stain - Haematoxylin Eosin) 36 Female 1937
7864 E., 24 Exc, Formol C-P Frontal 20 (Stain - Haematoxylin Eosin) 32.5 Male 1941
8553 E., 22 Exc Bouin C-P Transverse 12 (Stain - Haematoxylin Eosin) 38 Female 1947
9614 E,,22 5 Exc Bouin P Coronal 10 &15 Azan ? ? 1958 Rubella. Hysterectomy
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.

Stage21 bf8.jpg Stage21 bf9.jpg Stage21 bf10.jpg

Stage21 bf5.jpg Stage21 bf6.jpg Stage21 bf7.jpg

Stage21 bf2.jpg Stage21 bf3.jpg Stage21 bf4.jpg

Fig. 21-1. Photographs of three embryos belonging to stage 21. The superficial scalp vascular plexus of the head is plainly visible in several of these views, such as A. It has spread to a level more than halfway between an eye-ear line and the vertex of the head. The fingers are longer and show an early phase in the development of touch pads. These Tastballen are shown at higher magnification by Cummins (1929) at stage 20 (his fig. 7) and stage 22 (his fig. 8.) The hands are flexed at the wrists and are approaching each other over the cardiac region. The lower limbs are curving toward the median plane, and toes of the two feet make contact with each other in some specimens. Top row, No. 4090. Middle row, No. 8553. Bottom row, No 7392. All views are at the same magnification.

Size And Age

Most embryos of this stage measure 22–24 mm.

The age is believed to be approximately 52 postovulatory days.

External Form

The superficial vascular plexus of the head has spread upward to form a line at somewhat more than half the distance from eye-ear level to the vertex.

The fingers are longer and extend further beyond the ventral body wall than they did in the previous stage. The distal phalangeal portions appear slightly swollen and show the beginning of tactile pads. The hands are slightly flexed at the wrists and nearly come together over the cardiac eminence. The feet are also approaching each other, and the toes of the two sides sometimes touch.

Features For Point Scores

  1. Cornea. Cells are beginning to invade the postepithelial layer, converting it into the substantia propria (Streeter, 1951, fig. 16).
  2. Optic nerve. Remnants of ependyma are present and may extend along practically the whole length of the optic stalk. A hyaloid groove is visible at the bulbar end. A few nerve fibers are arriving at the brain.
  3. Cochlear duct. The tip of the duct now points definitely "downward" (fig. 19-6).
  4. Adenohypophysis. The thread-like stalk is beginning to be absorbed (fig. 19-7).
  5. Vomeronasal organ. The opening of the sac is reduced in size, a short, narrow neck is present, and the end of the sac is expanded (fig. 19-9).
  6. Submandibular gland. The duct has begun to form knob-like branches (fig. 19-10).
  7. Metanephros. Spoon-shaped glomerular capsules are developing, but no large glomeruli are present yet (fig. 19-11).
  8. Humerus. Cartilaginous phases 1-4 are present (Streeter, 1949, figs. 3, 19, and 20).

Additional Features

  • Heart. Some photomicrographs were reproduced by Cooper and O'Rahilly (1971, figs. 15-17).
  • Testis. The testis shows a flattened surface epithelium, an underlying tunica albuginea, and branching and anastomosing cords: "the forerunners of the seminiferous tubules" (Wilson, 1926a).
  • Brain. A general view of the organ was given by O'Rahilly and Gardner (1971, fig. 1). The olivary nucleus is present in the rhombencephalon. Three-quarters of the surface of the diencephalon is covered by the cerebral hemispheres. The optic tract reaches approximately the site of the lateral geniculate body. The insula can now be recognized as a faint concavity at the surface of the hemisphere.


References

Online Editor Note  
O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).

The original 1987 publication text, figures and tables have been altered in formatting, addition of internal online links, and links to PubMed. Original Document - Copyright © 1987 Carnegie Institution of Washington.

See also the later 2010 paper by the same authors - O'Rahilly R & Müller F. (2010). Developmental stages in human embryos: revised and new measurements. Cells Tissues Organs (Print) , 192, 73-84. PMID: 20185898 DOI.

Links: Embryonic Development | Carnegie Collection | Carnegie Embryos | Ronan O'Rahilly | Fabiola Müller



See also Müller F & O'Rahilly R. (1990). The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum. Anat. Embryol. , 182, 375-400. PMID: 2252222

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1987 Stages: Introduction | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | References | Appendix 1 | Appendix 2 | Historic Papers | Embryonic Development
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
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)



Cite this page: Hill, M.A. (2019, August 20) Embryology 1987 Developmental Stages In Human Embryos - Stage 21. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/1987_Developmental_Stages_In_Human_Embryos_-_Stage_21

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