in genetic overgrowth syndromes, such as Sotos syndrome, Beckwith-Wiedemann syndrome and Marshall-Smith syndrome. Bone maturation is delayed with the variation of normal development termed constitutional delay of growth and puberty, but delay also accompanies growth failure due to growth hormone deficiency and hypothyroidism. Recent studies show that organs like the liver can also be used to estimate age and sex, because of the unique feature of liver. Liver weight increases with age and is different between males and females. Thus, the liver can be employed in special medico-legal cases of skeletal deformities or mutilation. A table of possible causes of abnormal stature and the expected bone age associated with each condition is provided below. Physiology Formation of the human skeletal system begins in fetal life with the development of a loosely ordered connective tissue known as mesenchyme. The cells of the mesenchyme can become bone by one of two primary methods: (1) intramembranous ossification where mesenchymal cells differentiate directly into bone or (2) endochondral ossification where mesenchymal cells become a cartilaginous model of chondrocytes which then become bone. The bones of the limbs form and lengthen through endochondral ossification beginning by the 12th week after fertilization. At birth, only the metaphyses of the "long bones" are present. The long bones are those that grow primarily by elongation at an epiphysis at one end of the growing bone. The long bones include the femurs, tibias, and fibulas of the lower limb, the humeri, radii, and ulnas of the upper limb (arm + forearm), and the phalanges of the fingers and toes. The long bones of the leg comprise nearly half of adult height. The other primary skeletal component of height is the spine and skull. As a child grows the epiphyses become calcified and appear on x-rays, as do the carpal and tarsal bones of the hands and feet, separated on x-rays by a layer of invisible cartilage where most of the growth is occurring. As sex steroid levels rise during puberty, bone maturation accelerates. As growth nears conclusion and attainment of adult height, bones begin to approach the size and shape of adult bones. The remaining cartilaginous portions of the epiphyses become thinner. As these cartilaginous zones become obliterated, the epiphyses are said to be "closed" and no further lengthening of the bones will occur. A small amount of spinal growth concludes an adolescent's growth. The carpal bones arise from