Histochemical investigations on the symphysis menti in the human fetus related to fetal skeletal maturation in the hand and foot.

Histochemical investigations on the symphysis menti region were performed on 72 human embryos and fetuses of crown-rump lengths (CRL) ranging from 16 to 162 mm, presenting skeletal maturity indices (CNO = composite number of ossified bones in the hand and foot) ranging from 0-0 to 19-11. The symphysis menti region is described in five developmental stages according to morphology and histochemical reactions at the interzone, enchondral bone formation, and Meckel's cartilage. The stages are described according to histochemical reactions for glycosaminoglucuronoglycans, collagen, glycogen, alkaline and acid phosphatase, and non-specific AS esterase. Silver impregnation followed by X-ray and histochemical control for Ca++ deposits supplemented the study. Special attention was paid to a fusion of the bilateral Meckel's cartilages in the midline characteristic of stage II. This is a finding not previously recorded in human fetuses. It is suggested to designate this fusion 'the rostral connection'. Histochemically, the fusion appeared as ordinary cartilage matrix (chondroitin-4- and/or-6-sulphate). The absence of a rostral connection characteristic of stage III is discussed. On the basis of reactions for glycosaminoglycans and activity of hydrolytic enzymes, the symphysis is characterized as a growth zone, active in mandibular growth in width as well as in length, during the first half of the prenatal period. The material available did not justify a description of skeletal development in the symphysis menti as a function of CRL, of skeletal maturation in the hand and foot, or as a function of a combination of these parameters.