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
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)

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	Formalin	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	Formalin	P	Transverse	40	Al. coch.	38.5	Female	1914
1008	E, 26,4	Good	Formalin	P	Sagittal	40	Al. coch.	39	??	1914
1358F	E, 23	Good	Formalin	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	Formalin	P	Transverse	40	Al. coch.	30	Female	1922
4160	E,25	Poor	Formalin	P	Sagittal	25	(Stain - Haematoxylin Eosin)	39	Male	1923	Tubal
4960	E.22 Ch,, 47x42x28	Good	Formalin	P	Transverse	15	Al. coch., Mallory	31.5	Female	1925
5??6	E. 215	Good	Formalin	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,	Formalin	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.

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

Cornea. Cells are beginning to invade the postepithelial layer, converting it into the substantia propria (Streeter, 1951, fig. 16).
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.
Cochlear duct. The tip of the duct now points definitely "downward" (fig. 19-6).
Adenohypophysis. The thread-like stalk is beginning to be absorbed (fig. 19-7).
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).
Submandibular gland. The duct has begun to form knob-like branches (fig. 19-10).
Metanephros. Spoon-shaped glomerular capsules are developing, but no large glomeruli are present yet (fig. 19-11).
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
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)

Cite this page: Hill, M.A. (2024, April 25) 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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