UNSW Embryology

Human 12 Week Fetus

© Dr Mark Hill (2008)

Acknowledgements

Introduction

These images demonstrate early fetal period ossification occurring during in the head region.

Compare this 12 week fetus with the earlier 10 week Fetal and Carnegie stage embryos: size, head proportions, brain, head, skeletal development.

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

(Image: Virginia Diewert)

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. (More? Notes Skull | Face) Bony regions in the lower jaw (mandible) region also show spaces where tooth formation is occuring. (More? Tooth Development)

Medial View

(Image: Virginia Diewert)

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.

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 head view showing extensive nasal cartilage, nasal conchae, pituitary, secondary palate, oral cavity, tongue, mandible, hyoid, choana, oropharynx.

Note: Tongue musculature and mandibular attachment site.

Glossary of Terms

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UNSW Embryology ISBN: 978 0 7334 2609 4

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