<P> The long bones include the femora, tibiae, and fibulae of the legs; the humeri, radii, and ulnae of the arms; metacarpals and metatarsals of the hands and feet, the phalanges of the fingers and toes, and the clavicles or collar bones . The long bones of the human leg comprise nearly half of adult height . The other primary skeletal component of height are the vertebrae and skull . </P> <P> The outside of the bone consists of a layer of connective tissue called the periosteum . Additionally, the outer shell of the long bone is compact bone, then a deeper layer of cancellous bone (spongy bone) which contains in the medullary cavity the bone marrow . </P> <P> The outer shell of the long bone is made of cortical bone also known as compact bone . This is covered by a membrane of connective tissue called the periosteum . Beneath the cortical bone layer is a layer of spongy cancellous bone . Inside this is the medullary cavity which has an inner core of bone marrow made up of yellow marrow in the adult and red marrow in the child . </P> <P> There are two congenital disorders of the long bones . In a disorder known as rachitis fetalis anularis the ends of the long bones (epiphyses) are enlarged . Another disorder is known as rachitis fetalis micromelica in which there is a deficiency in the growth (as a shortness) of the bones . </P>

In adults most bone marrow in the long bones of the extremities contains