Talk:Carnegie stage 11

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A fifteen-somite human embryo

Adv Anat Embryol Cell Biol. 1989;116:1-102.

Mizoguti H.

Abstract

The morphological features of a well-preserved human embryo having 15 pairs of somites are described and illustrated with a complete set of photomicrographs. This embryo was found during a forensic dissection of a Japanese woman, fixed in 10% formalin for 5 days, and embedded in an epoxy resin mixture according to routine procedures. Serial sections about 0.75 microns thick were made and stained with toluidine blue. The most important features were as follows: 1. The embryo measured 4.1 mm in greatest length and was quite symmetrical viewed dorsally. 2. Closure of the neural tube took place from the level of the first branchial groove, corresponding to the level of the anterior one-third of the rhombencephalon, to that of about 0.4 mm posterior to the 15th somite, coming across the anterior end of the cloacal membrane. The neural plate and the wall of the neural tube consisted exclusively of a pseudostratified columnar epithelium, and neither the mantle nor marginal layers were identified anywhere. 3. At the anterior end of the embryo there was a conspicuous optic evagination, and at the dorsal end of the second branchial groove a round otic placode. 4. Of the three segments of the entodermal tract the midgut was the largest, constituting about half the entire length, and opened ventrally into the large yolk sac, whose surface was covered by a meshwork of highly developed blood vessels. In the foregut two branchial pouches were seen, corresponding to the branchial grooves. Primordia of the thyroid gland and of the liver were also recognized. Among the entodermal epithelial cells lining the ventral half of the hindgut anterior to the origin of the allantois were found numerous primordial germ cells. 5. Among the 15 pairs of somites, the first two were small and consisted of dermomyotome of epithelial cell arrangement and of sclerotome mingled into mesenchyme. The next three were large, triangular on transverse section, and consisted of dorsolateral dermomyotome and ventromedial sclerotome representing a densely packed mesenchymal cell aggregation. The sixth to the tenth somites showed a well-defined triangular contour, each containing a lumen, the myocoele. The last five somites were progressively smaller and were quadrangular in shape. 6. The intermediate mesoderm was encountered at levels from the 7th to the 15th somite, but no indications of pronephric differentiation were detected. 7. The heart tube was relatively large, took an S-shaped tortuous course, and occupied almost the entire pericardiac cavity. It consisted of the bulbus cordis, the ventriculus, and the atrium, each of which consisted of a thick myocardial tube and a thin endocardial tube.(ABSTRACT TRUNCATED AT 400 WORDS)

PMID 2610025

The development of the human brain and the closure of the rostral neuropore at stage 11

Anat Embryol (Berl). 1986;175(2):205-22.

Müller F, O'Rahilly R.

Abstract

Twenty embryos of stage 11 (24 days) were studied in detail and graphic reconstructions of twelve of them were prepared. The characteristic feature of this stage is 13-20 pairs of somites. The notochord sensu stricto appears first during this stage, and its rostral and caudal parts differ in origin. Rostrally, the notochordal plate is being transformed into the notochord in a caudorostral direction. The caudal part, however, arises from the axial condensation in the caudal eminence in a rostrocaudal direction. The caudal eminence (or end bud) represents the former primitive streak. The somites are increasing in number at a mean rate of 6.6 h per pair. The rostral neuropore closes towards the end of stage 11. The closure is basically bidirectional, being more rapid in the roof region and producing the embryonic lamina terminalis and future commissural plate in the basal region. The caudal neuropore is constantly open. The brain comprises telencephalon medium (represented by the embryonic lamina terminalis) and a series of neuromeres: 2 for the forebrain (D1 and D2), 1 for the midbrain, and 6-7 for the hindbrain (RhA-C; RhD is not clearly delineated). The forebrain still occupies a small proportion of the total brain, whereas the spinal part of the neural tube is lengthening rapidly. Some occlusion of the lumen of the neural tube was noted in 4 embryos, all of which had an open rostral neuropore. Hence there is at present no evidence that occlusion plays a role in expansion of the human brain. The marginal (primordial plexiform) layer is appearing, particularly in rhombomere D and in the spinal portion of the neural tube. The neural crest is still forming from both the (open) neural groove and the (closed) neural tube, and exclusively from both neural (including optic) and (mainly) otic ectoderm. The optic sulcus is now prominent, and its wall becomes transformed into the optic vesicle towards the end of stage 11. At this time also, an optic sheath derived from mesencephalic crest and optic crest is present. The mitotic figures of the optic neural crest are exceptional in being situated in the external part of the neural epithelium. The otic pit is becoming deeper, and its wall is giving rise to neural crest that is partly added to the faciovestibulocochlear ganglion and partly forms an otic sheath. The nasal plate does not yet give off neural crest. PMID 3826651


Carnegie Collection

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Carnegie Stage 11 Scanning EM Images

Carnegie Stage 11 Bright Field Images