How do bones form?

somite

one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo. Notochord into pieces

intramembranous ossification

process by which bone forms directly from mesenchymal tissue

intramembranous ossification

process by which bone forms directly from mesenchymal tissue . Occurs in the formation of the axial skeleton .

apical ectodermal ridge

A thickened area of ectoderm at the tip of a limb bud that promotes outgrowth of the limb bud.

limb buds

Clusters of mesenchyme cells

Bone formation and growth

During embryonic development a group of stem cells (messenchyme ) give rise to bones and cartilage .

Upper limb bud

Gives rise to bones of arms and hands appears at 4 weeks of development.

Lower limb buds

Gives rise to bones of the legs and foot

Mesenchyme

Group of stem cells give rise to bone and cartilage.

4 weeks of development

Lower limb bud gives rise to bones of the legs and foot

endochondral ossification

Process of transforming cartilage into bone.

Sclerotone

Somite grow bigger and split into several parts is called sclerotome . It is made up of undifferentiated cells called mesenchyme .

6 weeks of development

The mesenchyme of limb buds differentiate into hyaline cartilage. This forms a mold of different bones of the limbs

7 weeks of development

Upper limbs take 90 degree turn laterally causing the thumb to be rotated outward .lower limbs turn 90 degrees medically the big toe turn inwards .

Notochord

long supporting rod that runs through a chordate's body just below the nerve cord. Forms at 3 weeks of embryo development .

fontanelles

soft spots normally present on the skull of a newborn. Separated by areas of connective tissue . Important role during childbirth allows head to squeeze through .