Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Osteology, osteologia [the study of bones] - General Osteology
Development of the Skeleton

There are three stages of human Skeleton development: Connective Tissue (membranous), cartilaginous, and bony. In a 9 mm human embryo at 4–5 weeks of intrauterine development, pre-cartilaginous mesenchymal condensations corresponding to the connective tissue stage of development are clearly visible. By 2–3 months of intrauterine development, the mesenchyme transforms into Cartilage tissue, and the embryonic skeleton becomes cartilaginous. The only exceptions are the BONES OF THE cranial vault and the clavicle, which bypass the cartilaginous stage of development. The ossification process begins during this period. The first ossification centers appear in the jaws and clavicle at 2 months of development. Between 2 and 4 months of intrauterine development, most primary (diaphyseal) ossification centers are established in the diaphyses of tubular bones. Secondary epiphyseal ossification centers appear at the end of the prenatal period only in the distal femoral epiphysis and the proximal tibial epiphysis. In the epiphyses of all other bones, ossification centers form after birth.

A total of about 800 ossification centers develop in the skeleton, of which 120 emerge in the Skull bones, 295 in THE Vertebral Column, 101 in the Ribs, and 140 each in the bones of the upper and lower extremities (A. Andronescu, 1970). With the onset of Puberty, the bone elements within the bones fuse, and the epiphyseal cartilages are replaced by Bone tissue. By the age of 21–24, bone synostosis is complete, and they cease to grow in length. The Development of the skeleton is under the direct Influence of the Endocrine glands and The Nervous system.