UNSW Embryology

Facts: Week 10, 40 mm, female fetus, early fetal stage of development

The fetal period is a time of extensive growth in size and mass as well as differentiation of organ systems established in the embryonic period. In particular, the brain continues to grow and develop, the respiratory system differentiates, the urogenital system further differentiates between male/female, endocrine and gastrointestinal tract begins to function.

We will be looking at development within the fetus at this early stage by viewing sagittal plane images and considering their 3D relationships. It is not important to identify every structure within the fetus.

Observe the following features: organs, their anatomical location and relationships, axial skeleton, appendicular skeleton, CNS (brain and spinal cord), PNS (sensory ganglia), gastrointestinal tract (including herniation) and urogenital structures.

There are 4 separate sections of this fetus taken in the sagittal plane (moving from the right at Plane A towards the midline at Plane D).

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. (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

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.

(Images: Virginia Diewert)

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.

Link to next page in Fetal Practical - Fetal Period