Bone development in the fetus
This image demonstrates ossification in the fetus. Bone, colored brown/red, is the only tissue stained. Forming bone can readily be identified throughout the fetus, whether it was formed by intramembranous or endochondral ossification.
Flat bones >
The flat bones of the skull, formed by intramembranous ossification, are obvious.
Long bones >
The hyaline-cartilage template of the long bones was gradually replaced by bone (arrows) via endochondral ossification, beginning in the primary center of ossification and progressing toward both epiphyses. This process shows especially well in the left humerus and in the long bones of the right leg.
Hyaline cartilage >
The epiphyses of the forming bones are composed of hyaline cartilage that has not yet been replaced by bone. Later, secondary centers of ossification will form in these areas and this cartilage will also be replaced by bone.