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Glossary Bibliography Reprints Biographies Links Site Map Stages Table |
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Carnegie Stage |
Pairs of Somites |
Length (mm) |
Age (days)1 | Age (days)2 |
Features |
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| 1 | 1 | Fertilization |
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| 2 | 1.5-3 | 2-3 | From 2 to about 16 cells | |||
| 3 | 4 | 4-5 | Free blastocyst | |||
| 4 | 5-6 | 5-6 | Attaching blastocyst | |||
| 5 | 0.1-0.2 | 7-12 | 7-12 | Implanted although previllous | ||
| 5a | 0.1 | 7-8 | Solid trophoblast | |||
| 5b | 0.1 | 9 | Trophoblastic lacunae | |||
| 5c | 0.15-0.2 | 11-12 | Lacunar vascular circle | |||
| 6 | 0.2 | 13 | 13-15 | Chorionic villi; primitive streak may appear | ||
| 6a | Chorionic villi | |||||
| 6b | Primitive streak | |||||
| 7 | 0.4 | 16 | 15-17 | Notochordal process | ||
| 8 | 1.0-1.5 | 18 | 17-19 | Primitive pit, notochordal and neurenteric canals |
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| 9 | 1.2-2.5 | 20 | 19-21 | Somites first appear | ||
| 10 | 2-3.5 | 22 | 22-23 |
Neural folds begin to fuse, 2 pharyngeal bars, optic sulcus |
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| 11 | 2.5-4.5 | 24 | 23-26 | Rostral neuropore closes, optic vesicle | ||
| 12 | 3-5 | 26 | 26-30 | Caudal neuropore closes, 3 pharyngeal bars, upper limb buds appearing |
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| 13 | 4-6 | 28 | 28-32 | Four limb buds, lens disc, otic vesicle |
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| 14 | 5-7 | 32 | 31-35 | Lens pit and optic cup, endolymphatic appendage distinct |
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| 15 | 7-9 | 33 | 35-38 |
Lens vesicle, nasal pit,
antitragus beginning, hand plate, trunk relatively wider, cerebral vesicles |
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| 16 | 8-11 | 37 | 37-42 | Nasal pit faces ventrally, retinal pigment visible in intact embryo, auricular hillocks beginning, foot plate |
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| 17 | 11-14 | 41 | 42-44 | Head relatively larger, trunk straighter, nasofrontal groove distinct, auricular hillocks distinct, finger rays |
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| 18 | 13-17 | 44 | 44-48 | Body more cuboidal, elbow region and toe rays appearing, cyclids beginning, tip of nose distinct, nipples appear, ossification may begin |
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| 19 | 16-18 | 47.5 | 48-51 | Trunk elongating and straightening |
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| 20 | 18-22 | 50.5 | 51-53 | Upper limbs longer and bent at elbows |
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| 21 | 22-24 | 52 | 53-54 | Fingers longer, hands approach each other, feet likewise |
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| 22 | 23-28 | 54 | 54-56 |
Eyelids and external ear more developed |
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| 23 | 27-31 | 56.5 | 56-60 | Head more rounded, limbs longer and more developed |
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