Curriculum Module
Axial Skeleton Development
The axial skeleton forms the skull, vertebral column, ribs, and sternum. It develops from paraxial mesoderm (somites), lateral plate mesoderm, and neural crest cells through both intramembranous and endochondral ossification.
Membranous Neurocranium
The Neurocranium protects the brain. Its membranous flat bones form directly from mesenchyme via Intramembranous Ossification, visible as needle-like bone spicules.
In the newborn skull, flat bones are separated by Sutures. Points where multiple bones intersect form wide gaps called Fontanelles.
The Chondrocranium forms the skull base. Prechordal cartilages (neural crest) and chordal cartilages (occipital somites) fuse and ossify endochondrally.
Key Insight
This stage is critical for embryonic support structures and establishes the main body axis.