DIE ENTSTEHUNG VON SPALTWIRBELN BEI DANFORTH’S SHORT-TAIL MAUS

Abstract

The development of split vertebrae in homozygous Sd[long dash]-mice can be traced back to the mesenchymal stage. The condensation of the sclerotomic cells in the midline is delayed. Consequently the dorso-ventral diameter of the cartilaginous bodies is measurably reduced. A hypothesis is made suggesting that the presence of the notochord influences the formation of the mesenchymal anlagen of the vertebral bodies. The premature degeneration of the notochord affects, therefore, the definitive organization of the centra. Splitting is localized in the caudal region of the vertebral column and is frequently indicated in the cranial region. A possible explanation for this differential regional splitting is proposed. Luxation of the headjoints is an indirect effect of this genetic disturbance. Formation of the headjoint ligaments starts normally and becomes defective later on. Parts of these ligaments disappear. The parts that remain develop atypically due to the altered shape of the headjoints. The presence of the Sd-factor also clarifies the fact that the dens Epistrophei has a double origin.