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.
Vertebrae & Ribs
Sclerotome derivatives form vertebrae via Resegmentation, permitting myotome muscles to bridge intervertebral discs. The Notochord dissolves locally but expands in discs to become the Nucleus Pulposus, surrounded by circular fibers of the Annulus Fibrosus.
Primary curvatures (thoracic and sacral) form first; secondary curvatures (cervical and lumbar) form later as the child holds their head and learns to walk. Bony Ribs arise from paraxial sclerotome costal processes, while costal cartilages and the Sternum (manubrium, sternebrae, xiphoid) derive from lateral plate mesoderm.
Key Insight
This stage is critical for embryonic support structures and establishes the main body axis.