Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent segments.
Transverse section of a human embryo of the third week to show the differentiation of the primitive segment. (Kollmann.) ao. Aorta. m.p. Muscle-plate. n.c. Neural canal. sc. Sclerotome. s.p. cutis-plate.
A sclerotome is part of a somite, a structure in vertebrate embryonic development. Sclerotomes eventually differentiate into the vertebrae and most of the skull. The caudal (inferior/lower) half of one sclerotome fuses with the rostral (superior/upper) half of the adjacent one to form each vertebra.
From their initial location within the somite, the sclerotome cells migrate medially towards the notochord. These cells meet the sclerotome cells from the other side to form the vertebral body. From this vertebral body, sclerotome cells move dorsally and surround the developing spinal cord, forming the vertebral arch. Other cells move distally to the costal processes of thoracic vertebrae to form the ribs.