Final answer:
The development of the skeletal system begins with mesenchyme, leading to the formation of bone tissue through the differentiation of mesenchymal cells into osteoblasts. The appendicular skeleton originates from mesenchymal cells within limb buds, which later become hyaline cartilage models of bones. The axial skeleton starts with the notochord, somites, and sclerotomes, which form the connective tissues, cartilages, and bones of the body.
Step-by-step explanation:
The developmental stages of bone begin with mesenchyme, an embryonic tissue. Initially, mesenchymal cells gather and differentiate into specialized cells, with some becoming capillaries and others transforming into osteogenic cells, which then become osteoblasts. These early osteoblasts cluster in what is known as an ossification center. By the end of this process, the embryonic skeleton starts to form structured bone tissue.
In the limbs, the appendicular skeleton originates from this mesenchyme. Limb buds are visible at the end of the fourth week of development, and by the sixth week, these buds start to differentiate into hyaline cartilage, which forms models of future bones. As development progresses, the upper and lower limbs rotate to reach their final positions. In addition, the processes by which mesenchyme gives rise to bone are completed before birth, leading to the formation of the joint interzone and the future joint cavity.
During embryonic development, the axial skeleton also begins to form with the appearance of the notochord and development of somites, eventually giving rise to fibrous connective tissues, cartilages, and bones.