The main factors in the formation of bones are function, heredity, the action of gravity, nutritional conditions, their topography in the skeleton, movements in a gravitational field, etc. When strengthening the function of the bone, they increase in size, when weakening it, they change their structure and lose strength properties.
Bone development. Different bones are formed differently. A small part of the bones develops from the connective tissue of the mesenchyme, for example, individual bones of the skull (parietal, temporal, frontal, etc.), most of the bones develop at the site of the cartilage. Blood vessels grow in the cartilaginous anlage of the bone, and osteoblasts grow with them. Ossification centers arise, osteoclasts destroy cartilage, and osteoblasts form bone tissue in its place. Due to changes in power stresses in a growing body, part of the newly formed bone is also destroyed by osteoclasts. As a result of such a complex growth process, a compact and spongy bone substance is formed.
The process of ossification in the tubular bones begins in the diaphysis, and then goes on to the pineal gland. The epiphyses are connected for some time with the diaphysis by the epiphyseal growth plate. Epiphyseal cartilage stiffens with age. The process of ossification ends at the end of the growth of the animal. The size of the epiphyseal cartilage and ossification centers can determine the age of young animals. In place of the spongy substance during the growth process, a bone cavity is formed in the diaphysis of the tubular bones, which is filled with bone marrow.