Pith nucleus grows in fetal later period and infantile period very fast, have inside pith nucleus many and mucous qualitative, there is bunch inside, into bundle notochord cell composition.

• 髓核在胎儿后期及婴儿时期生长很快，在髓核内有大量粘液间质，内有成簇、成束的脊索细胞组成。