Fetal Development - 12 Weeks

From Embryology

Introduction

Week 12 or clinical age GA week 14.

Images on this current page show head ossification occurring during the early fetal period (12 weeks approx 92 mm CRL in size). The head undergoes two different forms of ossification (endochondral and intramembranous) in separate regions of the skull. Furthermore the two images (lateral and medial) identify regions of cartilage development. Compare this 12 week fetus with the earlier 10 week Fetal and Carnegie stage embryos: size, head proportions, brain, head, skeletal development.

12 Week Images: Sagittal unlabeled | Sagittal labeled | Sagittal medial view | Sagittal lateral view | Pituitary unlabeled | Pituitary labeled | Tongue | Skull Development | Head Development
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Historic Embryology  
1940 Fetus Physiology
Carnegie Fetal: 95 | 96 | 142 | 145 | 184 | 211 | 217 | 300 | 362 | 448 | 449 | 538 | 590 | 607 | 625 | 662 | 693 | 847 | 858 | 922 | 928 | 948 | 972 | 1318 | 1388 | 1455 | 1591 | 1597b | 1656 | 1686 | 2250a | 2250b | 3990 | 5652 | 6581 | 7218

12 week Head

These are 2 views of the same 12 week 92 mm CRL human fetus head, double stained to show both cartilage (blue) and newly-formed bone (red).

Lateral View

In this lateral (external) view, note the distribution of new bone in the plates of the cranial vault, temporal bone, orbit, upper jaw (maxilla) and lower jaw (mandible) regions. Bony regions in the lower jaw (mandible) region also show spaces where tooth formation is occurring.

Fetal head lateral.jpg

Medial View

In this medial (internal) view, note the distribution of cartilage from the nasal region through the base of the skull to the atlas/axis (with new bone forming). See also the original Meckel's cartilage within the newly forming bony mandible.

Fetal head medial.jpg

Mandible

Selected extract of above images showing 2 views (lateral/external left, medial/internal right) of the mandible region.

Note: Cartilage in the neck where the hyoid bone will eventually form. Meckel's cartilage visible in the medial view within the newly forming bone.

Nose and Mouth

Selected medial head view showing key features of head musculoskeletal and neurological development. Note extensive nasal cartilage, nasal conchae, pituitary, secondary palate, oral cavity, tongue, mandible, hyoid, choana, oropharynx.

Fetal head section 01.jpg


Carnegie Embryos - Sensenig (1951) - Spinal Cord Meninges 
Age Group
(gestation age)
Embryo
no.
Crown Rump
Length
Thickness of
sections (microns)
Plane of
section
Illustration
12 weeks 1455 78.5 50 Sagittal
172 80.0 100 Transverse
Template:CE72181 80.0 20 Transverse Figs. 17, 18, pl. 3
  • Number of somites given in parentheses.
  • T. transverse; F. frontal or coronal: S. sagittal.
  • Embryo loaned by Department of Embryology. Carnegie Institution of Washington. prepared for study on a U. S. Public Health Service Grant.

References


Sensenig EC. The early development of the meninges of the spinal cord in human embryos. (1951) Contrib. Embryol., Carnegie Inst. Wash. Publ. 611,


Reviews

Articles

{{#pmid:19049908]]

Wilkin H, Tuohy J & Theewis W. (2000). Prenatal diagnosis of fragile X and Turner mosaicism in a 12-week fetus. Prenat. Diagn. , 20, 854-5. PMID: 11038471

Robb A, Forsyth L & Tolmie J. (1987). Partial trisomy 17q and a generalised bone dysplasia in a 12 week fetus. J. Med. Genet. , 24, 502-4. PMID: 3656375


Search PubMed

Note: Week 12 post-fertilization age (used throughout this current website) is Gestational Age GA Week 14 (LMP). Searches for clinical Week 14 gestational age will match this post-fertilization age.

Search PubMed Now: week 12 fetus | week 14 fetus

Terms

choana - the posterior nasal aperture which is the passageway from the back of one side of the nose to the throat. There are two choanae, one on either side of the nose.

mandible

nasal conchae - the thin scroll-shaped bony elements forming three groove-like air passages/chambers in the nasal cavities.

oropharynx - the oral (within the mouth) part of the pharynx which extends from the uvula to the level of the hyoid bone.

Also note the developing tongue musculature and its mandibular attachment site.

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Cite this page: Hill, M.A. (2019, May 25) Embryology Fetal Development - 12 Weeks. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fetal_Development_-_12_Weeks

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G