Embryology of the Vertebral Column and Ribs

Vertebrae are segmentally repeated because of the primary segmentation of the myotomes.

In its development, the endoskeleton typically passes through two stages: mesenchyme and bone.

The mesenchymal stage is also known as the membranous stage.

In lower vertebrates, the endoskeleton may remain wholly or partly ossified.

Calcified cartilage is commonly found in most vertebrates during development.

Bone produced by replacing pre-existing cartilage is known as membranous bone.

Investigation of the vertebrate skeleton development shows that all bones arise directly from the mesenchyme.

The accumulation of mesenchyme in the skeletogenous regions signifies the beginning of the cartilage stage in endoskeleton development.

In most vertebrates, the cartilage is entirely replaced by bone during development.

The skeleton is said to be ossified when it retains its cartilaginous composition.