Appendicular skeleton:
During the 5th week of development, the limbs start to appear as buds from the ventrolateral body wall. Each bud includes a mesenchymal core that derived from the somatic layer of the lateral plate mesoderm. During the 6th week, the mesenchymal bone models in the limbs undergo chondrification to form cartilaginous models.
By the end of 8th week, primary ossification centers begin to appear in the shafts (diaphysis) of some cartilaginous models. By the 12th week, this primary ossification centers have appeared in almost all long bones of the limbs. The ossification progresses gradually from the primary centers toward the ends of the cartilaginous model. At birth, the diaphysis of the model is completely ossified. The first bones in the body begin to ossify are the clavicles. After birth, secondary ossification centers start to appear in the ends of bones (epiphysis) especially in the knee bone, and all these epiphyses become ossified during the first 2 years.
However, a plate of cartilage called epiphyseal cartilage plate (epiphyseal growth plate) remains temporarily between the diaphysis and each epiphysis (this plate is important in growth of the bone length).
*Around age of 20, this plate ossifies and the epiphyses unite with the diaphysis and this result allows no more growth.
By the end of 8th week, primary ossification centers begin to appear in the shafts (diaphysis) of some cartilaginous models. By the 12th week, this primary ossification centers have appeared in almost all long bones of the limbs. The ossification progresses gradually from the primary centers toward the ends of the cartilaginous model. At birth, the diaphysis of the model is completely ossified. The first bones in the body begin to ossify are the clavicles. After birth, secondary ossification centers start to appear in the ends of bones (epiphysis) especially in the knee bone, and all these epiphyses become ossified during the first 2 years.
However, a plate of cartilage called epiphyseal cartilage plate (epiphyseal growth plate) remains temporarily between the diaphysis and each epiphysis (this plate is important in growth of the bone length).
*Around age of 20, this plate ossifies and the epiphyses unite with the diaphysis and this result allows no more growth.