Category:Carnegie Stage 12

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Carnegie Stage 12

This Embryology category shows pages and media related to embryonic development in week 4, 26 - 30 days, GA week 6. The embryos have a crown rump length (CRL) of 3 - 5 mm and somite number 21 - 29 pairs.

There is also a specific Carnegie stage 12 resource page.

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Embryo Examples

Sorted by Somite Number

  • 22 somites - Girgis embryo, Royal School of Medicine, Cairo. Apparently a normal embryo, studied and reconstructed by the wax-plate method at the Institute of Anatomy, University College, London by Girgis (1926). [1]Otic vesicle and caudal neuropore both still open. Three pharyngeal arches are present. Umbilical vesicle opens rather widely into gut. Morphology of central nervous system, digestive system, vascular system, and excretory system described in detail. The specimen had been kept in alcohol for a prolonged period, and apparently is not suitable for cytological minutiae.
  • 22 somites - Carnegie No. 8963 (University of Chicago No. H 1093). Described by Wen (1928) with particular reference to the nervous system.
  • 23 somites - Van den Broek embryo “A,” Zentral-Institut für Hirnforschung, Amsterdam.Two similar embryos are described together by Van den Broek (1911). The description refers almost * entirely to “A,” which is the better preserved of the two. It is evidently normal, and judging from the form of the brain, open otocyst, and liver it corresponds to about a 23-somite embryo, although it is said to have 21–22 somites.
  • 23 somites - R Meyer, No. 300. The Meyer collection was transferred from Berlin to the University of Zürich in 1922, and placed in charge of H. Frey. This valuable specimen was described in monographic form by Thompson (1907, 1908). Also described and figured in the Keibel and Elze Normentafein (1908). It constitutes a type specimen.
  • 23 somites - Hertwig embryo “Wolff II,” Anatomisches-biologisches Institut, Berlin. Normal, well-preserved specimen, having three pharyngeal arches and no trace of rostral neuropore. Described by Keibel and Elze (1908). Specimen has been reconstructed.
  • 23 somites - Carnegie No. 8964 (University of Chicago No. H 984). Described by Wen (1928) with particular reference to the nervous system.
  • 24 somites - Johnson, Harvard Collection, Boston. Complete description, based on many models and histological study, published in monographic form by Johnson (1917). Rostral and caudal neuropores closed. Otic vesicle retains a narrow opening to surface. Three pharyngeal arches are present. Hepatic trabeculae invading framework of liver. Umbilical vesicle is compressed rostrocaudally, i.e., early umbilical stalk. Probably originally 25 somites (Arey, 1938).
  • 24 somites - Homo Nürnberger, Anatomisches Institut, Universität Köln. Described in detail and excellently illustrated by Rosenbauer (1955), with particular reference to the cardiovascular system.
  • 25 somites - West embryo, University College, Cardiff. A 3-mm embryo much like the Johnson specimen and a good representative of the middle period of this stage (West, 1937)[2]. By means of profile and wax reconstructions the main organ systems are outlined, including an excellent study of the nephric system. The success attained by West in the orientation of his sections and the consequent accuracy in profile outlines is explained by the stained margins of the squarely trimmed paraffin block, which served as guides.
  • 25 somites - Carnegie No. 6097. A graphic reconstruction was published by Müller and O'Rahilly (1980a).
  • 26 somites - His embryo M, Basel, H. h. 1. One of the group of embryos carefully studied by His for surface anatomy, and then cut in serial sections for microscopical examination, setting a new standard in human embryology (His, 1880–1885). From the development of the liver, lungs, heart, brain, and otocysts, and the absence of upper limb buds, it is estimated that it belongs in the 26-somite group.
  • 27 somites - described by Waterston (1914)[3]
  • 28 somites - His embryo Lr., Leipzig No. 67. Although used to good purpose by His, this specimen is probably not entirely normal (His, 1880–1885). The estimate of 28 somites is based on the narrowed umbilical stalk and the beginning upper limb buds.
  • 28 somites - Hammar embryo (Nystroem), Anatomisches Institut, Uppsala. Described by Hammar in Keibel and Elze (1908). Digestive system described by Forssner (1907). The number of somites given above is estimated on the basis of three pharyngeal arches, full convex back, small opening in otic vesicles to surface, hepatic trabeculae, and appearance of section through cardiac region. Central nervous system shows folding of wall which characterizes imperfect preservation. External form appears normal.
  • 28 somites - von Spee collection, Kiel. Sketches published in Döderlein's Handbuch (1915). Reported to have 31 somites - but absence of upper limb buds and the fact that the otic vesicles are still open to the surface makes it probable that an estimate of 28 somites is more nearly correct.
  • 28–29 somites - Carnegie No. 148. Described by Gage (1905). Perhaps 29–30 somites (Arey, 1938).
  • 29 somites - 20–21-day Coste embryo. Specimen not sectioned, but the exquisite drawings contained in Coste's atlas, Développement des corps organisés, Paris (1849), reveal many details of the surface form of this well-preserved embryo. In form it resembles closely Carnegie No. 1062, 29 somites - including rounded back curve, trace of upper limb buds, compressed gut-umbilical vesicle junction, size of hepatic area, form of cardiac tube, presence of otic pore, and outlines of head. Four pharyngeal arches are shown, but the fourth may have been an exaggeration of the depression lying caudal to the third bar. Also the somitic count seems to exceed the 29 estimated, but this may be caused by overemphasis on partial divisions of the terminal somitic ridge. In size its greatest length is about 4 mm. If it were straightened out as much as No. 1062, it would probably be close to 4.5 mm, like the latter.
  • 29 somites - Janošík, Royal Bohemian University, Prague. Somitic count estimated on the following characteristics: three pharyngeal arches, closure of rostral and caudal neuropores, detachment of otocyst from surface, definite lung bud, elongated hepatic diverticulum with gut epithelium proliferating into adjacent tissue, narrowed umbilical stalk, and well-developed mesonephric duct and tubules. The main features of the vascular system are clearly shown. There were two embryos in this case, one of which was definitely stunted. The above description refers to the normal embryo Janošík, 1887).
  • 29 somites - Waterston, University of St. Andrews, Fife. Specimen reported as having 27 paired somites (Waterston, 1914). In several characteristics it appears to be transitional between stages 12 and 13. Probably more than 27 somites - perhaps 28 (Arey, 1938) or 29. Among its advanced structures are prominent lung buds, large primordium of liver with extensive invasion by gut epithelium, narrow umbilical stalk, elongated median thyroid, and advanced ear vesicles. The upper limb buds were not prominent on the surface but stand out clearly in the sections. The blood vessels are everywhere greatly distended with blood cells, which is probably a peculiarity of this particular specimen.

Unknown Somite Number

  • Harvard No. 714, 4-mm embryo. Described in detail by Bremer (1906). Probably belongs to stage 12 rather than stage 11 or stage 13. It shows some unusual features, such as arrested or delayed closure of the rostral neuropore.
  • No. 102 and No. 126, Department of Anatomy, Tohoku University, Sendai. These two embryos were assigned to stage 12 but the somitic count is not given. Distribution of alkaline phosphatase was studied by Mori (1965). PMID 14291749


  1. Girgis A. Description of a Human Embryo of Twenty-two paired Somites J. Anat.: 1926, 60(Pt 4);382-410. PMID 17104111 | PMC1249865
  2. C M West A Human Embryo of Twenty-five Somites. J. Anat.: 1937, 71(Pt 2);169-200.1 PubMed 17104635 PMC1252340
  3. D Waterston A Human Embryo of Twenty-seven Pairs of somites - Embedded in Decidua. J Anat Physiol: 1914, 49(Pt 1);90-118 PMID 17233016 | PMC1288995

Pages in category ‘Carnegie Stage 12’

The following 68 pages are in this category, out of 68 total.

Media in category ‘Carnegie Stage 12’

The following 10 files are in this category, out of 210 total.

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